Mercer County, North Dakota: History
The Dakota Territory legislature enacted a January 8, 1873 law to create a county named Mercer, whose boundaries would be identical to Pratt (a now-extinct county). This county did not come into existence, as the 1873 act was nullified on January 14, 1875, by the legislature. On that date the legislature created another Mercer County, from previously unorganized territory. The county was named for William Henry Harrison Mercer, (1844–1901), a rancher who settled north of Bismarck in 1869. The unorganized county was not attached to another county for judicial or administrative purposes; this condition continued until November 6, 1883, when the county government was organized.
The county boundaries were altered in 1879, 1881, 1885, 1892, and 1901. Its boundaries have remained unchanged since 1901.