The Dakota Territory legislature created the county on January 4, 1873, naming it for Civil War General Philip Henry Sheridan. The county organization was not completed at that time, but the new county was not attached to another county for administrative or judicial purposes. In 1883 and again in 1887, the county boundaries were reduced, and on November 8, 1892, the county was dissolved, its remaining territory assigned to McLean. This lasted until the November 3, 1908 election, when McLean County voters chose to partition off the eastern portion of that unit into a new county, although the new boundaries were somewhat different from the former Sheridan. The new county government was effected on December 24 of that year.
