Flint Hill is a town in northwestern St. Charles County, Missouri, United States. The population was 525 at the 2010 census. Flint Hill was officially founded in 1838 by Captain Taliferro P. Grantham. The community took its name from Flint Hill, Rappahannock County, Virginia, the native home of a share of the first settlers. A post office called Flint Hill has been in operation since 1836.