List of U.S. Counties Named After Rivers - M

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• Mahoning County, Ohio: Mahoning is named for the Mahoning River.
• Malheur County, Oregon: Malheur is named for the Malheur River.
• Manistee County, Michigan was named for the Manistee River, which in turn had Native American name meaning river at whose mouth there are islands.
• Maries County, Missouri: Maries is named from the Maries River.
• Merrimack County, New Hampshire: Merrimack is named for the Merrimack 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.