Ohio County was formed in 1798 from land taken from Hardin county. Ohio was the 35th county in the state of Kentucky in order of formation. It was named after the Ohio River, which originally formed its northern boundary, but it lost its northern portions in 1829 when the counties of Daviess and Hancock were formed. In January 1865, during the American Civil War, the courthouse in Hartford was burned. However, the county records were removed first and preserved. Ohio County has a total area of 596 square miles with a population count of just over 24, 000 residents.