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. Due to the county's government complex spanning 2 municipalities, its county sea…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. Due to the county's government complex spanning 2 municipalities, its county seat is shared between Pontiac and Waterford. 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.