Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 03, 2021	Jun. 30, 2020
Cover page.
Entity Registrant Name	CITIZENS FINANCIAL SERVICES, INC.
Entity Central Index Key	0000739421
Current Fiscal Year End Date	--12-31
Document Type	10-K
Amendment Flag	false
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Document Transition Report	false
Entity File Number	0-13222
Entity Incorporation, State or Country Code	PA
Entity Tax Identification Number	23-2265045
Entity Address, Address Line One	15 South Main Street
Entity Address, City or Town	Mansfield
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	16933
City Area Code	570
Local Phone Number	662-2121
No Trading Symbol Flag	true
Title of 12(b) Security	Common Stock, par value $1.00 per share
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 173,044,000
Entity Common Stock, Shares Outstanding		3,913,732