Caldwell is a city in Sumner County, Kansas, United States. As of the 2010 census, the city population was 1,068.
In 1887, the Chicago, Kansas and Nebraska Railway built a branch line north-south from Herington to Caldwell. This branch line connected Herington, Lost Springs, Lincolnville, Antelope, Marion, Aulne, Peabody, Elbing, Whitewater, Furley, Kechi, Wichita, Peck, Corbin, Wellington, Caldwell. This branch line was extended to Pond Creek, Oklahoma in 1888, and connected Caldwell, Renfrow, Medford, Jefferson (the original Pond Creek). By 1893, it was incrementally built to Fort Worth, Texas. This railroad foreclosed in 1891 and taken over by Chicago, Rock Island and Pacific Railway, which shut down in 1980 and reorganized as Oklahoma, Kansas and Texas Railroad, merged in 1988 with Missouri Pacific Railroad, merged in 1997 with Union Pacific Railroad. Most locals still refer to this railroad as the "Rock Island".
Caldwell is located at 37°2′3″N 97°36′32″W / 37.03417°N 97.60889°W / 37.03417; -97.60889 (37.034077, -97.609022). According to the United States Census Bureau, the city has a total area of 1.1 square miles (2.8 km²), all of it land.