Mercer is a city in McLean County, North Dakota, United States. The population was 94 at the 2010 census.Mercer was founded in 1905 along a now-abandoned branch line of the Northern Pacific Railway extending from Carrington to Turtle Lake. The name comes from William Henry Harrison Mercer, a well known rancher in the Missouri River Valley for many years and for whom Mercer County is also named.The city of Mercer lies on North Dakota Highway 200 between Underwood and McClusky.