Originally named Clackamas District, it was one of the four original Oregon districts created by Oregon's Provisional Legislature on July 5, 1843 along with Twality (later Washington), Champooick (later Marion), and Yamhill. The four districts were redesignated as counties in 1845. At the time of its creation, Clackamas County covered portions of four present-day U.S. states and a Canadian province. The Columbia River became the northern boundary of the county in 1844. Soon after John McLoughlin staked a land claim in Oregon City and built a house that in 2003 became a unit of the Fort Vancouver National Historic Site.