Maries River. Merrimack County, New Hampshire: Merrimack is named for the Merrimack River. Mississippi County, Arkansas: Mississippi is named for the Mississippi River. Mississippi County, Missouri: Mississippi is named after the Mississippi River. Moniteau County, Missouri: Montineau is named after Moniteau Creek. Monongalia County, West Virginia: Monongalia is named for the Monongahela River. Muskegon County, Michigan is named for the Muskegon River, named for the Ojibwa language word meaning swamp or marsh. Musselshell County, Montana: Musselshell is named for the Musselshell River, named in turn by the Lewis and Clark Expedition presumably due to mussels found on its banks. N 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. O Oconee County, Georgia: Oconee is named for the Oconee River that forms part of the county's border Ohio County, Indiana: Ohio is named for the Ohio River. Ohio County, Kentucky: Also named for the Ohio River. When the county was formed, the river formed its northern boundary, but no longer does after several new counties were carved from it. Ohio County, West Virginia: Also named for the Ohio River. Ontonagon County, Michigan is named for a river called Nantounagon on an early French map. Otter Tail County, Minnesota: Otter Tail is named after Otter Tail Lake and Otter Tail River. The river was named by the Ojibwa for its long sandbar shaped like an otter's tail. Osage County, Kansas: Osage is named for the Osage River. Oswego County, New York: Oswego is named for the Oswego River. Ouachita County, Arkansas: Ouachita is named for the Ouachita River. Ouachita Parish, Louisiana: named for the Ouachita River P Payette County, Idaho: Payette is named after the Payette River, which, in turn, is named for explorer Francois Payette. Pearl River County, Mississippi: Named for the Pearl River, obviously Pecos County, Texas: Pecos [pey-kuhs] is named after the Pecos River. The name "Pecos" derives from the Keresan (Native American language) term for the Pecos Pueblo, [p'æyok'ona]. Platte County, Nebraska: Platte is