Mercer County is the name of several counties in the United States:
Mercer County, New Jersey, the most populous U.S. county named Mercer and home to New Jersey's capital city, Trenton
Mercer County, Illinois
Mercer County, Kentucky
Mercer County, Missouri
Mercer County, North Dakota
Mercer County, Ohio
Mercer County, Pennsylvania
Mercer County, Virginia, has existed twice; the two counties continue in existence with the same name in Kentucky and West Virginia
Mercer County, West Virginia