The 23,000-square-mile (60,000 km2) Matanuska-Susitna Borough (the Alaskan equivalent of a county) governs the Mat-Su Valley. According to the 2010 Census, the borough's population is 88,995, a 50% increase since 2000. The Mat-Su Valley was originally inhabited by Athabaskan people and was explored by Russians in 1818.