Circleville is a city in and the county seat of Pickaway County, Ohio, United States, along the Scioto River. The population was 13,314 at the 2010 census.The city's name is derived from its originally layout after 1810 within the 1,100 ft diameter of a circle of a Hopewell tradition earthwork dating to the early centuries of the Common Era. The county courthouse was built in the center of the innermost circle. By the late 1830s residents had tired of this design and gained authorization from the state legislature to change the layout to a standard grid, which was accomplished by the mid-1850s. All traces of the Hopewell earthwork were destroyed here, although hundreds of other monuments may be found in the Ohio Valley.