The county was established on March 1, 1827, by the Indiana General Assembly. It was named for Dr. Joseph Warren, who was killed in 1775 at the Battle of Bunker Hill, in which he fought as a private because his commission as a general had not yet taken effect. The short-lived town of Warrenton was the original Warren County seat, chosen by commissioners in March 1828; the next year an act was passed calling for the seat to be relocated, and in June 1829 it was moved to Williamsport.