FORM 4 [ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).         
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      
1. Name and Address of Reporting Person * CAVANAGH RICHARD 2. Issuer Name and Ticker or Trading Symbol BLACKROCK MUNICIPAL INCOME INVESTMENT TRUST [ BBF ] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable)__X__ Director                    _____ 10% Owner
_____ Officer (give title below)    _____ Other (specify below)
(Last)         (First)         (Middle)
55 EAST 52ND STREET
3. Date of Earliest Transaction (MM/DD/YYYY)
4/12/2021
(Street)
NEW YORK, NY 10055
(City)       (State)       (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)
 
6. Individual or Joint/Group Filing (Check Applicable Line) _X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. Code
(Instr. 8)
4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)
6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V Amount (A) or (D) Price
Common Stock  4/12/2021    J(1)    487  D  (1) 0  D   

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. Trans. Code
(Instr. 8)
5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
6. Date Exercisable and Expiration Date 7. Title and Amount of Securities Underlying Derivative Security
(Instr. 3 and 4)
8. Price of Derivative Security
(Instr. 5)
9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Explanation of Responses:
(1)  Effective as of April 12, 2021, BlackRock Municipal Income Investment Trust (the "Target Fund") was reorganized into BlackRock Municipal Income Trust II (the "Acquiring Fund"). In the Reorganization, common shareholders of the Target Fund received common shares of the Acquiring Fund having a value equal to the aggregate NAV of the Target Fund common shares surrendered as determined at the close of business on April 9, 2021, less the costs of the Reorganization. As of April 9, 2021, the Target Fund reported a NAV per share of $14.3831 and the Acquiring Fund reported a NAV per share of $15.0242. The conversion ratio for the Target Fund's common shares was 0.95732884. In the Reorganization, Richard E. Cavanagh received 466 common shares (and cash for fractional shares, if any) of the Acquiring Fund in exchange for his 487 common shares of the Target Fund.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
CAVANAGH RICHARD
55 EAST 52ND STREET
NEW YORK, NY 10055
X



Signatures
/s/ Dean A. Caruvana as Attorney-in-Fact 4/14/2021
**Signature of Reporting Person Date
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