Sparta is a city in Randolph County, Illinois, United States. The population was 4,095 at the 2020 census. The city was the principal filming locat…Sparta is a city in Randolph County, Illinois, United States. The population was 4,095 at the 2020 census. The city was the principal filming location for the 1967 film In the Heat of the Night. Consumer ammunition manufacturer Underwood Ammo is headquartered and solely based in Sparta.