v3.26.1
Document And Entity Information
Jun. 30, 2026
Document Information [Line Items]  
Entity, Registrant Name FIRST NORTHERN COMMUNITY BANCORP
Document, Type 8-K
Document, Period End Date Jun. 30, 2026
Entity, File Number 000-30707
Entity, Incorporation, State or Country Code CA
Entity, Tax Identification Number 68-0450397
Entity, Address, Address Line One 195 N First Street
Entity, Address, City or Town Dixon
Entity, Address, State or Province CA
Entity, Address, Postal Zip Code 95620
City Area Code 707
Local Phone Number 678-3041
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security FNRN
Trading Symbol FNRN
Security Exchange Name NASDAQ
Entity, Emerging Growth Company false
Amendment Flag false
Entity, Central Index Key 0001114927