Stockton is a city in Cedar County, Missouri, United States. The population was 1,683 at the 2020 census. It is the county seat of Cedar County. …Stockton is a city in Cedar County, Missouri, United States. The population was 1,683 at the 2020 census. It is the county seat of Cedar County. Stockton was platted in 1846. It was originally named Lancaster, but was renamed Fremont in 1847 in honor of John C. Frémont. In 1857 it was renamed again, in honor of Robert F. Stockton.