Item A.1. Information about the Registrant.

a. Name of Registrant	BlackRock Municipal Income Investment Trust
b. Investment Company Act file number for Registrant: (e.g., 811-______)	811-10333
c. CIK number of Registrant	0001137392
d. LEI of Registrant	A2HHML4IABXGDVD17F46

e. Address and telephone number of Registrant.

Street Address 1	100 Bellevue Parkway
Street Address 2
City	Wilmington
State, if applicable
Foreign country, if applicable
Zip / Postal Code	19809
Telephone number	800-441-7762

Item A.2. Information about the Series.

a. Name of Series.	BlackRock Municipal Income Investment Trust
b. EDGAR series identifier (if any).
c. LEI of Series.	A2HHML4IABXGDVD17F46

Item A.3. Reporting period.

a. Date of fiscal year-end.	2021-07-31
b. Date as of which information is reported.	2020-10-31

Item A.4. Final filing

Does the Fund anticipate that this will be its final filing on Form N PORT?

Yes

No

Report the following information for the Fund and its consolidated subsidiaries.

Item B.1. Assets and liabilities. Report amounts in U.S. dollars.

a. Total assets, including assets attributable to miscellaneous securities reported in Part D.	231501419.14
b. Total liabilities.	38311796.98
c. Net assets.	193189622.16

Item B.2. Certain assets and liabilities. Report amounts in U.S. dollars.

a. Assets attributable to miscellaneous securities reported in Part D.	0.00000000
b. Assets invested in a Controlled Foreign Corporation for the purpose of investing in certain types of instruments such as, but not limited to, commodities.	0.00000000

c. Borrowings attributable to amounts payable for notes payable, bonds, and similar debt, as reported pursuant to rule 6-04(13)(a) of Regulation S-X [17 CFR 210.6-04(13)(a)].

Amounts payable within one year.
Banks or other financial institutions for borrowings.	0.00000000
Controlled companies.	0.00000000
Other affiliates.	0.00000000
Others.	0.00000000
Amounts payable after one year.
Banks or other financial institutions for borrowings.	35368392.35000000
Controlled companies.	0.00000000
Other affiliates.	0.00000000
Others.	0.00000000

d. Payables for investments purchased either (i) on a delayed delivery, when-issued, or other firm commitment basis, or (ii) on a standby commitment basis.

(i) On a delayed delivery, when-issued, or other firm commitment basis:	1979359.25000000
(ii) On a standby commitment basis:	0.00000000
e. Liquidation preference of outstanding preferred stock issued by the Fund.	52000000.00000000
f. Cash and cash equivalents not reported in Parts C and D.	152358.73000000

Item B.3. Portfolio level risk metrics.

If the average value of the Fund's debt securities positions for the previous three months, in the aggregate, exceeds 25% or more of the Fund's net asset value, provide:

Currency Metric: 1
ISO Currency code	United States Dollar

a. Interest Rate Risk (DV01). For each currency for which the Fund had a value of 1% or more of the Fund’s net asset value, provide the change in value of the portfolio resulting from a 1 basis point change in interest rates, for each of the following maturities: 3 month, 1 year, 5 years, 10 years, and 30 years.

Maturity period.
3 month.	632.09000000
1 year.	5519.33000000
5 years.	37992.46000000
10 years.	62959.20000000
30 years.	74516.10000000

b. Interest Rate Risk (DV100). For each currency for which the Fund had a value of 1% or more of the Fund’s net asset value, provide the change in value of the portfolio resulting from a 100 basis point change in interest rates, for each of the following maturities: 3 month, 1 year, 5 years, 10 years, and 30 years.

Maturity period.
3 month.	50842.64000000
1 year.	459686.54000000
5 years.	3623896.33000000
10 years.	6300516.10000000
30 years.	7419574.16000000

c. Credit Spread Risk (SDV01, CR01 or CS01). Provide the change in value of the portfolio resulting from a 1 basis point change in credit spreads where the shift is applied to the option adjusted spread, aggregated by investment grade and non-investment grade exposures, for each of the following maturities: 3 month, 1 year, 5 years, 10 years, and 30 years.

Investment grade.
Maturity period.
3 month.	45688.14000000
1 year.	1781.28000000
5 years.	38091.67000000
10 years.	22466.47000000
30 years.	11476.87000000
Non-Investment grade.
Maturity period.
3 month.	2315.23000000
1 year.	904.20000000
5 years.	20231.70000000
10 years.	4396.23000000
30 years.	3513.91000000

For purposes of Item B.3., calculate value as the sum of the absolute values of:
(i) the value of each debt security,
(ii) the notional value of each swap, including, but not limited to, total return swaps, interest rate swaps, and credit default swaps, for which the underlying reference asset or assets are debt securities or an interest rate;
(iii) the notional value of each futures contract for which the underlying reference asset or assets are debt securities or an interest rate; and
(iv) the delta-adjusted notional value of any option for which the underlying reference asset is an asset described in clause (i),(ii), or (iii).

Report zero for maturities to which the Fund has no exposure. For exposures that fall between any of the listed maturities in (a) and (b), use linear interpolation to approximate exposure to each maturity listed above. For exposures outside of the range of maturities listed above, include those exposures in the nearest maturity.

Item B.4. Securities lending.

a. For each borrower in any securities lending transaction, provide the following information:

b. Did any securities lending counterparty provide any non-cash collateral?

Yes

No

Item B.5. Return information.

a. Monthly total returns of the Fund for each of the preceding three months. If the Fund is a Multiple Class Fund, report returns for each class. Such returns shall be calculated in accordance with the methodologies outlined in Item 26(b) (1) of Form N-1A, Instruction 13 to sub-Item 1 of Item 4 of Form N-2, or Item 26(b) (i) of Form N-3, as applicable.

Monthly Total Return Record: 1
Monthly total returns of the Fund for each of the preceding three months – Month 1.	-0.82000000
Monthly total returns of the Fund for each of the preceding three months – Month 2.	-0.12000000
Monthly total returns of the Fund for each of the preceding three months – Month 3.	-0.34000000
b. Class identification number(s) (if any) of the Class(es) for which returns are reported.

c. For each of the preceding three months, monthly net realized gain (loss) and net change in unrealized appreciation (or depreciation) attributable to derivatives for each of the following categories: commodity contracts, credit contracts, equity contracts, foreign exchange contracts, interest rate contracts, and other contracts. Within each such asset category, further report the same information for each of the following types of derivatives instrument: forward, future, option, swaption, swap, warrant, and other. Report in U.S. dollars. Losses and depreciation shall be reported as negative numbers.

Asset category.

Interest Rate Contracts

Monthly net realized gain(loss) – Month 1	0.00000000
Monthly net change in unrealized appreciation (or depreciation) – Month 1	0.00000000

Monthly net realized gain(loss) – Month 2	0.00000000
Monthly net change in unrealized appreciation (or depreciation) – Month 2	0.00000000

Monthly net realized gain(loss) – Month 3	0.00000000
Monthly net change in unrealized appreciation (or depreciation) – Month 3	90471.57000000

Instrument type.

Future

Monthly net realized gain(loss) – Month 1	0.00000000
Monthly net change in unrealized appreciation (or depreciation) – Month 1	0.00000000

Monthly net realized gain(loss) – Month 2	0.00000000
Monthly net change in unrealized appreciation (or depreciation) – Month 2	0.00000000

Monthly net realized gain(loss) – Month 3	0.00000000
Monthly net change in unrealized appreciation (or depreciation) – Month 3	90471.57000000

d. For each of the preceding three months, monthly net realized gain (loss) and net change in unrealized appreciation (or depreciation) attributable to investment other than derivatives. Report in U.S. dollars. Losses and depreciation shall be reported as negative numbers.
Month 1

Monthly net realized gain(loss) – Month 1	-27821.15000000
Monthly net change in unrealized appreciation (or depreciation) – Month 1	-1770797.80000000

Month 2

Monthly net realized gain(loss) – Month 2	8330.63000000
Monthly net change in unrealized appreciation (or depreciation) – Month 2	-703437.22000000

Month 3

Monthly net realized gain(loss) – Month 3	105209.83000000
Monthly net change in unrealized appreciation (or depreciation) – Month 3	-1251597.68000000

Item B.6. Flow information.

Provide the aggregate dollar amounts for sales and redemptions/repurchases of Fund shares during each of the preceding three months. If shares of the Fund are held in omnibus accounts, for purposes of calculating the Fund's sales, redemptions, and repurchases, use net sales or redemptions/repurchases from such omnibus accounts. The amounts to be reported under this Item should be after any front-end sales load has been deducted and before any deferred or contingent deferred sales load or charge has been deducted. Shares sold shall include shares sold by the Fund to a registered unit investment trust. For mergers and other acquisitions, include in the value of shares sold any transaction in which the Fund acquired the assets of another investment company or of a personal holding company in exchange for its own shares. For liquidations, include in the value of shares redeemed any transaction in which the Fund liquidated all or part of its assets. Exchanges are defined as the redemption or repurchase of shares of one Fund or series and the investment of all or part of the proceeds in shares of another Fund or series in the same family of investment companies.

Month 1

a. Total net asset value of shares sold (including exchanges but excluding reinvestment of dividends and distributions).	0.00000000
b. Total net asset value of shares sold in connection with reinvestments of dividends and distributions.	0.00000000
c. Total net asset value of shares redeemed or repurchased, including exchanges.	0.00000000

Month 2

a. Total net asset value of shares sold (including exchanges but excluding reinvestment of dividends and distributions).	0.00000000
b. Total net asset value of shares sold in connection with reinvestments of dividends and distributions.	0.00000000
c. Total net asset value of shares redeemed or repurchased, including exchanges.	0.00000000

Month 3

a. Total net asset value of shares sold (including exchanges but excluding reinvestment of dividends and distributions).	0.00000000
b. Total net asset value of shares sold in connection with reinvestments of dividends and distributions.	0.00000000
c. Total net asset value of shares redeemed or repurchased, including exchanges.	0.00000000

Item B.7. Highly Liquid Investment Minimum information.

a. If applicable, provide the Fund's current Highly Liquid Investment Minimum.
b. If applicable, provide the number of days that the Fund's holdings in Highly Liquid Investments fell below the Fund's Highly Liquid Investment Minimum during the reporting period.
c. Did the Fund's Highly Liquid Investment Minimum change during the reporting period?	Yes No N/A

Item B.8. Derivatives Transactions.

For portfolio investments of open-end management investment companies, provide the percentage of the Fund's Highly Liquid Investments that it has segregated to cover or pledged to satisfy margin requirements in connection with derivatives transactions that are classified among the following categories as specified in rule 22e-4 [17 CFR 270.22e-4]:

(1) Moderately Liquid Investments
(2) Less Liquid Investments
(3) Illiquid Investments
Classification

NPORT-P: Part C: Schedule of Portfolio Investments

For each investment held by the Fund and its consolidated subsidiaries, disclose the information requested in Part C. A Fund may report information for securities in an aggregate amount not exceeding five percent of its total assets as miscellaneous securities in Part D in lieu of reporting those securities in Part C, provided that the securities so listed are not restricted, have been held for not more than one year prior to the end of the reporting period covered by this report, and have not been previously reported by name to the shareholders of the Fund or to any exchange, or set forth in any registration statement, application, or report to shareholders or otherwise made available to the public.

Item C.1. Identification of investment.

a. Name of issuer (if any).	Chicago O'Hare International Airport
b. LEI (if any) of issuer. In the case of a holding in a fund that is a series of a series trust, report the LEI of the series.	T5UYO5SYLC8K73MJQX30
c. Title of the issue or description of the investment.	CHICAGO IL O'HARE INTERNATIONAL ARPT REVENUE
d. CUSIP (if any).	167593GF3

At least one of the following other identifiers:

Identifier.	ISIN
ISIN	US167593GF31

Item C.2. Amount of each investment.

Balance. Indicate whether amount is expressed in number of shares, principal amount, or other units. For derivatives contracts, as applicable, provide the number of contracts.

Balance	4345000.00000000
Units	Principal amount
Description of other units.
Currency. Indicate the currency in which the investment is denominated.	United States Dollar
Value. Report values in U.S. dollars. If currency of investment is not denominated in U.S. dollars, provide the exchange rate used to calculate value.	4388623.80000000
Exchange rate.
Percentage value compared to net assets of the Fund.	2.271666433699

Item C.3. Indicate payoff profile among the following categories (long, short, N/A). For derivatives, respond N/A to this Item and respond to the relevant payoff profile question in Item C.11.

Payoff profile.

Long

Short

N/A

Item C.4. Asset and issuer type. Select the category that most closely identifies the instrument among each of the following:

Asset type (short-term investment vehicle (e.g., money market fund, liquidity pool, or other cash management vehicle), repurchase agreement, equity-common, equity-preferred, debt, derivative-commodity, derivative-credit, derivative-equity, derivative-foreign exchange, derivative-interest rate, derivatives-other, structured note, loan, ABS-mortgage backed security, ABS-asset backed commercial paper, ABS-collateralized bond/debt obligation, ABS-other, commodity, real estate, other). If “other,” provide a brief description.

Debt

Issuer type (corporate, U.S. Treasury, U.S. government agency, U.S. government sponsored entity, municipal, non-U.S. sovereign, private fund, registered fund, other). If “other,” provide a brief description.

Municipal

Item C.5. Country of investment or issuer.

Report the ISO country code that corresponds to the country where the issuer is organized.	UNITED STATES OF AMERICA
If different from the country where the issuer is organized, also report the ISO country code that corresponds to the country of investment or issuer based on the concentrations of the risk and economic exposure of the investments.

Item C.6. Is the investment a Restricted Security?

Is the investment a Restricted Security?

Yes

No

Item C.7.

a. Liquidity classification information. For portfolio investments of open-end management investment companies, provide the liquidity classification(s) for each portfolio investment among the following categories as specified in rule 22e-4 [17 CFR 270.22e-4]. For portfolio investments with multiple liquidity classifications, indicate the percentage amount attributable to each classification.

i. Highly Liquid Investments

ii. Moderately Liquid Investments

iii. Less Liquid Investments

iv. Illiquid Investments

Category.

N/A

b. If attributing multiple classification categories to the holding, indicate which of the three circumstances listed in the Instructions to Item C.7 is applicable.

Instructions to Item C.7 Funds may choose to indicate the percentage amount of a holding attributable to multiple classification categories only in the following circumstances: (1) if portions of the position have differing liquidity features that justify treating the portions separately; (2) if a fund has multiple sub-advisers with differing liquidity views; or (3) if the fund chooses to classify the position through evaluation of how long it would take to liquidate the entire position (rather than basing it on the sizes it would reasonably anticipated trading). In (1) and (2), a fund would classify using the reasonably anticipated trade size for each portion of the position.

Item C.8. Indicate the level within the fair value hierarchy in which the fair value measurements fall pursuant to U.S. Generally Accepted Accounting Principles (ASC 820, Fair Value Measurement). [1/2/3] Report “N/A” if the investment does not have a level associated with it (i.e., net asset value used as the practical expedient).

Indicate the level within the fair value hierarchy in which the fair value measurements fall pursuant to U.S. Generally Accepted Accounting Principles 7(ASC 820, Fair Value Measurement). [1/2/3] Report "N/A" if the investment does not have a level associated with it (i.e., net asset value used as the practical expedient).

1

2

3

N/A

Item C.9. For debt securities

For debt securities, also provide:

a. Maturity date.

2041-01-01

b. Coupon.

i. Select the category that most closely reflects the coupon type among the following (fixed, floating, variable, none).	Fixed
ii. Annualized rate.	6.50000000
c. Currently in default? [Y/N]	Yes No
d. Are there any interest payments in arrears or have any coupon payments been legally deferred by the issuer? [Y/N]	Yes No
e. Is any portion of the interest paid in kind? [Y/N] Enter "N" if the interest may be paid in kind but is not actually paid in kind or if the Fund has the option of electing in-kind payment and has elected to be paid in-kind.	Yes No

f. For convertible securities, also provide:

i. Mandatory convertible? [Y/N]	Yes No
ii. Contingent convertible? [Y/N]	Yes No

iii. Description of the reference instrument, including the name of issuer, title of issue, and currency in which denominated, as well as CUSIP of reference instrument, ISIN (if CUSIP is not available), ticker (if CUSIP and ISIN are not available), or other identifier (if CUSIP, ISIN, and ticker are not available).
If other identifier provided, indicate the type of identifier used.

v. Delta (if applicable).

Item C.10. For repurchase and reverse repurchase agreements, also provide:

a. Select the category that reflects the transaction (repurchase, reverse repurchase). Select "repurchase agreement" if the Fund is the cash lender and receives collateral. Select "reverse repurchase agreement" if the Fund is the cash borrower and posts collateral.

Repurchase Reverse repurchase is not checked

Reverse repurchase

b. Counterparty.

i. Cleared by central counterparty? [Y/N] If Y, provide the name of the central counterparty.

Yes

No

ii. If N, provide the name and LEI (if any) of counterparty.

c. Tri-party?	Yes No
d. Repurchase rate.
e. Maturity date.

f. Provide the following information concerning the securities subject to the repurchase agreement (i.e., collateral). If multiple securities of an issuer are subject to the repurchase agreement, those securities may be aggregated in responding to Items C.10.f.i-iii.

Item C.11. For derivatives, also provide:

Item C.12. Securities lending.

a. Does any amount of this investment represent reinvestment of cash collateral received for loaned securities?

Yes

No

b. Does any portion of this investment represent that is treated as a Fund asset and received for loaned securities?

Yes

No

c. Is any portion of this investment on loan by the Fund?

Yes

No

NPORT-P: Part C: Schedule of Portfolio Investments

For each investment held by the Fund and its consolidated subsidiaries, disclose the information requested in Part C. A Fund may report information for securities in an aggregate amount not exceeding five percent of its total assets as miscellaneous securities in Part D in lieu of reporting those securities in Part C, provided that the securities so listed are not restricted, have been held for not more than one year prior to the end of the reporting period covered by this report, and have not been previously reported by name to the shareholders of the Fund or to any exchange, or set forth in any registration statement, application, or report to shareholders or otherwise made available to the public.

Item C.1. Identification of investment.

a. Name of issuer (if any).	Tobacco Settlement Financing Corp/VA
b. LEI (if any) of issuer. In the case of a holding in a fund that is a series of a series trust, report the LEI of the series.	N/A
c. Title of the issue or description of the investment.	TOBACCO SETTLEMENT FING CORP VA
d. CUSIP (if any).	88880NAU3

At least one of the following other identifiers:

Identifier.	ISIN
ISIN	US88880NAU37

Item C.2. Amount of each investment.

Balance. Indicate whether amount is expressed in number of shares, principal amount, or other units. For derivatives contracts, as applicable, provide the number of contracts.

Balance	1010000.00000000
Units	Principal amount
Description of other units.
Currency. Indicate the currency in which the investment is denominated.	United States Dollar
Value. Report values in U.S. dollars. If currency of investment is not denominated in U.S. dollars, provide the exchange rate used to calculate value.	1009979.80000000
Exchange rate.
Percentage value compared to net assets of the Fund.	0.522791953681

Item C.3. Indicate payoff profile among the following categories (long, short, N/A). For derivatives, respond N/A to this Item and respond to the relevant payoff profile question in Item C.11.

Payoff profile.

Long

Short

N/A

Item C.4. Asset and issuer type. Select the category that most closely identifies the instrument among each of the following:

Asset type (short-term investment vehicle (e.g., money market fund, liquidity pool, or other cash management vehicle), repurchase agreement, equity-common, equity-preferred, debt, derivative-commodity, derivative-credit, derivative-equity, derivative-foreign exchange, derivative-interest rate, derivatives-other, structured note, loan, ABS-mortgage backed security, ABS-asset backed commercial paper, ABS-collateralized bond/debt obligation, ABS-other, commodity, real estate, other). If “other,” provide a brief description.

Debt

Issuer type (corporate, U.S. Treasury, U.S. government agency, U.S. government sponsored entity, municipal, non-U.S. sovereign, private fund, registered fund, other). If “other,” provide a brief description.

Municipal

Item C.5. Country of investment or issuer.

Report the ISO country code that corresponds to the country where the issuer is organized.	UNITED STATES OF AMERICA
If different from the country where the issuer is organized, also report the ISO country code that corresponds to the country of investment or issuer based on the concentrations of the risk and economic exposure of the investments.

Filer CIK	0001137392
Filer CCC	********
Filer Investment Company Type
Is this a LIVE or TEST Filing?	LIVE TEST
Would you like a Return Copy?
Is this an electronic copy of an official filing submitted in paper format?

NPORT-P: Filer Information

Submission Contact Information

Notification Information

NPORT-P: Part A: General Information

Item A.1. Information about the Registrant.

Item A.2. Information about the Series.

Item A.3. Reporting period.

Item A.4. Final filing

NPORT-P: Part B: Information About the Fund

Item B.1. Assets and liabilities. Report amounts in U.S. dollars.

Item B.2. Certain assets and liabilities. Report amounts in U.S. dollars.

Item B.3. Portfolio level risk metrics.

Item B.4. Securities lending.

Item B.5. Return information.

Item B.6. Flow information.

Item B.7. Highly Liquid Investment Minimum information.

Item B.8. Derivatives Transactions.

NPORT-P: Part C: Schedule of Portfolio Investments

Item C.1. Identification of investment.

Item C.2. Amount of each investment.

Item C.3. Indicate payoff profile among the following categories (long, short, N/A). For derivatives, respond N/A to this Item and respond to the relevant payoff profile question in Item C.11.

Item C.4. Asset and issuer type. Select the category that most closely identifies the instrument among each of the following:

Item C.5. Country of investment or issuer.

Item C.6. Is the investment a Restricted Security?

Item C.7.

Item C.9. For debt securities

Item C.10. For repurchase and reverse repurchase agreements, also provide:

Item C.11. For derivatives, also provide:

Item C.12. Securities lending.

NPORT-P: Part C: Schedule of Portfolio Investments

Item C.1. Identification of investment.

Item C.2. Amount of each investment.

Item C.3. Indicate payoff profile among the following categories (long, short, N/A). For derivatives, respond N/A to this Item and respond to the relevant payoff profile question in Item C.11.

Item C.4. Asset and issuer type. Select the category that most closely identifies the instrument among each of the following:

Item C.5. Country of investment or issuer.

Item C.6. Is the investment a Restricted Security?

Name
Phone
E-Mail Address

Notify via Filing Website only?
Series ID

SEC Form N filed