Warren County is a county in the U.S. state of Indiana. It lies in the western part of the state between the Illinois state line and the Wabash River. According to the 2020 census, it had a population of 8,440. Its county seat is Williamsport. Before the arrival of non-indigenous settlers in the early 19th century, the area was inhabited by several Native American tribes. The county was officially established in 1827 and was the 55th county to be formed in Indiana.