Durham is the core of the four-county Durham-Chapel Hill Metropolitan Area in North Carolina. It is the county seat of Durham County, though portions also extend into Wake County in the east and Orange County in the west. As the fourth-largest city in the state, and the 85th-largest in the United States by population, Durham is the home of Duke University and North Carolina Central University, and is also one of the vertices of the Research Triangle area (home of the Research Triangle Park).