Marion County is located in the U.S. state of Indiana. The 2020 United States census reported a population of 977,203, making it the 54th-most populous county in the U.S., the most populous county in the state, and the main population center of the 11-county Indianapolis–Carmel–Greenwood MSA in central Indiana. Indianapolis is the county seat, the state capital, and most populous city. Marion County is consolidated with Indianapolis through an arrangement known as Unigov.