Belleville is a city in and the county seat of Republic County, Kansas, United States. As of the 2020 census, the population of the city was …Belleville is a city in and the county seat of Republic County, Kansas, United States. As of the 2020 census, the population of the city was 2,007. Belleville was founded in 1869, and incorporated as a city in 1878. It was named for Arabelle Tutton, the wife of a member of the town company.