The Republican River takes its name from the Republican Pawnees,who lived on its bank until about 1815. Lewis and Clark mention the stream in their diaries in 1804.

The Republican River is 550 miles long. The North Fork begins in a pasture southwest of Wray Colorado. The South Fork begins east of Limon Colorado. The two forks meet near Benkelman Nebraska and wind thru Trenton, Mc Cook, Cambridge, Franklin, Red Cloud and Superior Nebraska before flowing back into Kansas. The Republican continues south thru Concordia and joins the Smoky Hill River to form the Kansas River near Junction City Kansas. Important tributaries of the Republican are the Arickaree River and Whiteman's creek of Colorado, the Redwillow creek of Nebraska and the Beaver, Sappa and Prairies Dog creeks of Kansas. Lakes fed by the Republican River are used for recreation and flood control. They include Bonnie Dam in Colorado, Trenton and Harlan County Lakes in Nebraska and Milford Lake in Kansas. The stream at Clay Center has been dammed and the power utilized.

The Republican is a slow-flowing river, approximately 2 mph. The hot, dry weather of the plains, intensive irrigation practices and about 19 inches of annual rainfall affect the water levels of the river and its tributaries. Flash floods can cause the river to rise, but flooding downsteam is contained by dams and floodplains.