Lancaster is a city in Atchison County, Kansas, United States. As of the 2020 census, the population of the city was 246. Lancaster was platt…Lancaster is a city in Atchison County, Kansas, United States. As of the 2020 census, the population of the city was 246. Lancaster was platted in 1857. It may have been named after Lancaster, Pennsylvania. Lancaster was an early contender for county seat. Lancaster was a station on the Missouri Pacific Railroad.