Nemaha County jail and sheriff's residence, now occupied by the Nemaha County Historical Society, at southeast corner of 6th and Nemaha Streets in Seneca, Kansas; seen from the southwest, looking obliquely across 6th. – Ammodramus, CC0 – Wikimedia Commons Nemaha County is located in Kansas. About 10,273 people live here (as of 2020). Between 2010 and 2020, the population grew from 10,178 to 10,273. The area covers about 1,863.0 square kilometers. The region is divided into 7 Municipalities. The region was founded in 1855. The name originates from Nemaha River basin (River basin) Nemaha County is county in Kansas, United States. More information at www.Nemaha.KansasGov.com.