Statement of Changes in Beneficial Ownership (4)

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 ^* Warren Brian	2. Issuer Name and Ticker or Trading Symbol CoreSite Realty Corp [ COR ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) SVP, Engineering & Product
(Last) (First) (Middle) C/O CORESITE REALTY CORPORATION, 1001 17TH STREET, SUITE 500	3. Date of Earliest Transaction (MM/DD/YYYY) 3/15/2021
(Street) DENVER, CO 80202 (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)
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock	3/15/2021		A		3751 ⁽¹⁾	A	$0.00	25152	D
Common Stock	3/15/2021		A		4375 ⁽²⁾	A	$0.00	29527	D
Common Stock	3/15/2021		S⁽³⁾		300 ⁽⁴⁾	D	$115.58 ⁽⁵⁾	29227	D
Common Stock	3/15/2021		S⁽³⁾		600 ⁽⁴⁾	D	$116.97 ⁽⁶⁾	28627	D
Common Stock	3/15/2021		S⁽³⁾		956 ⁽⁴⁾	D	$117.92 ⁽⁷⁾	27671	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)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)			11. Nature of Indirect Beneficial Ownership (Instr. 4)

Explanation of Responses:
(1)	Represents restricted stock granted under the issuer's Amended and Restated 2010 Equity Incentive Award Plan (the "2010 Plan"). The restricted stock vests in three equal annual installments beginning on March 15, 2022, provided that the reporting person remains in continuous service with the issuer as of each vesting date.
(2)	Represents performance-based restricted shares ("PSAs") granted under the 2010 Plan. The number of PSAs earned is based on the issuer's achievement of relative total shareholder return ("TSR") measured versus the MSCI US REIT Index over a three-year performance period ending December 31, 2023, and the number of shares earned may range from 25% to 175%. The PSAs are earned as follows: (i) 20% of the PSAs are earned upon TSR achievement in year one of the performance period, (ii) 20% of the PSAs are earned upon TSR achievement in year two of the performance period, (iii) 20% of the PSAs are earned upon TSR achievement in year three of the performance period, and (iv) 40% of the PSAs are earned upon a cumulative TSR achievement over the three-year performance period, subject to the reporting person's continued service with the issuer at the end of the three-year performance period. The PSAs are granted and issued at 175% of the target amount.
(3)	The shares were sold pursuant to a sales plan adopted by the reporting person and intended to comply with Rule 10b5-1 under the Securities Exchange Act of 1934.
(4)	Represents shares sold by the reporting person to cover tax obligations upon the vesting of restricted stock.
(5)	The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $115.28 to $116.02, inclusive. The reporting person undertakes to provide to the issuer, any shareholder of the issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnotes 5 through 7.
(6)	The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $116.43 to $117.36, inclusive.
(7)	The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $117.59 to $118.28, inclusive.

Reporting Owners
Reporting Owner Name / Address	Relationships
Reporting Owner Name / Address	Director	10% Owner	Officer	Other
Warren Brian C/O CORESITE REALTY CORPORATION 1001 17TH STREET, SUITE 500 DENVER, CO 80202			SVP, Engineering & Product