v3.26.1
Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2025
Mar. 27, 2026
Jun. 30, 2025
Document And Entity Information      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 000-21344    
Entity Registrant Name FIRST KEYSTONE CORPORATION    
Entity Incorporation, State or Country Code PA    
Entity Tax Identification Number 23-2249083    
Entity Address, Address Line One 111 West Front Street    
Entity Address, City or Town Berwick    
Entity Address, State or Province PA    
Entity Address, Postal Zip Code 18603    
City Area Code 570    
Local Phone Number 752-3671    
Title of 12(g) Security Common Stock, par value $2.00 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    
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 84,792,940
Entity Common Stock, Shares Outstanding   6,272,135  
Documents Incorporated by Reference [Text Block]

Portions of the Registrant’s 2026 definitive Proxy Statement are incorporated by reference in Part III of this Report.

    
Auditor Name Baker Tilly US, LLP    
Auditor Location Milwaukee, Wisconsin    
Auditor Firm ID 23    
Entity Central Index Key 0000737875    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Amendment Flag false