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- Nemaha County, Kansas: Nemaha is named for the Nemaha River.
- Nemaha County, Nebraska: Nemaha is named for Nimaha, the Oto name meaning miry water for a stream which crossed the county and emptied into the Missouri River.
- Neosho County, Kansas: Neosho is named for the Neosho River.
- Niobrara County, Wyoming: Niobrara is named for the Niobrara River. Niobrara is Omaha for flat or broad river.
- Nodaway County, Missouri: Nodaway is named from the Nodaway River. Nodaway is a Potawatomi word meaning placid.
Read more about this topic: List Of U.S. Counties Named After Rivers