Oakland County is a county in the U.S. state of Michigan. It is a principal county of the Detroit metropolitan area, containing the bulk of Detroit's northern suburbs. Its county seat is Pontiac, and its largest city is Troy. As of the 2020 Census, its population was 1,274,395, making it the second-most populous county in Michigan, and the largest county in the United States without a city of 100,000 residents.