Born in East Mahoning Township, Indiana County, Pennsylvania to Henry and Elizabeth (Thompson) Vanhorn, he moved to Pomeroy, Ohio in 1844, studied law and was admitted to the bar about 1850. He moved to Kansas City in 1855, was a member of the board of aldermen in 1857; postmaster of Kansas City 1857-1861 Van Horn purchased the newspaper The Enterprise in 1856 and renamed it The Kansas City Journal, which published daily from 1858 until its closing in 1942. Van Horn was elected mayor of Kansas City to three terms, in 1861, 1863, and 1864.