ATLAN′TIC. A city, the county-seat of Cass County, Iowa, 82 miles west-southwest of Des Moines, on the Chicago, Rock Island and Pacific Railroad (Map: Iowa, B 3). It has starch works, machine-shops, and other manufactures. Atlantic was incorporated in 1869; by the existing charter the mayor holds office for two years and the city council consists of eight members. Population, in 1890, 4351; in 1900, 5046.