Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 11, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	0-6233
Entity Registrant Name	1st Source Corporation
Entity Incorporation, State or Country Code	IN
Entity Tax Identification Number	35-1068133
Entity Address, Address Line One	100 North Michigan Street
Entity Address, City or Town	South Bend,
Entity Address, State or Province	IN
Entity Address, Postal Zip Code	46601
City Area Code	574
Local Phone Number	235-2000
Title of 12(b) Security	Common Stock — without par value
Trading Symbol	SRCE
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 906,733,159
Entity Common Stock, Shares Outstanding		24,750,203
Documents Incorporated by Reference	Portions of the 2022 Proxy Statement for the 2022 annual meeting of shareholders to be held April 21, 2022, are incorporated by reference into Part III.
Entity Central Index Key	0000034782
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
ICFR Auditor Attestation Flag	true