Preble county is located in southwestern Ohio on the Indiana state line just west of Dayton and calls Eaton its county seat. The county population on July 1, 1999, was 43,472, an increase of 3,359 over the 1990 census.
Natural features of the county include Fourmile, Sevenmile and Twins Creeks which flow from north to south, Rush Run Lake to the south and Acton Lake, which is the anchor for Hueston Woods State Park, to the southwest.