Circleville is a city in and the county seat of Pickaway County, Ohio, United States, along the Scioto River. The population was 13,485 at the 2000 census. Noted frontier explorer Christopher Gist was the first recorded European visitor to the Circleville area. Gist reached "Maguck," a small town of about 10 families on the east bank of the Scioto River and the south side of Circleville, on January 20, 1751, and remained in the town until January 24. Circleville was founded in 1810. It derived its name from the circular portion of a large Hopewell culture earthwork upon which it was built. The original town plan integrated Circleville into the preexisting land with a street layout of concentric circles. An octagonal courthouse stood directly in the center. Dissatisfaction rose with Circleville’s layout, however, and in 1837, the Ohio General Assembly authorized the "Circleville Squaring Company" to convert it into a square. By 1856, this had been completed in several phases. No remaining traces of the original earthworks remain, though a few old buildings retain curved walls that were part of the original circular layout.