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