Washington Township is one of the nine townships of Marion County, Indiana, located in the northern part of the county. The township is entirely within the city of Indianapolis. The population as of the 2020 census was 138,678, up from 132,049 at the 2010 census. The first settlement at Washington Township was made in 1819.

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 most populous county in the state and the 54th-most populous county in the U.S. Indianapolis is the county seat, the state capital, and most populous city. Marion County is consolidated with Indianapolis through an arrangement known as Unigov. Marion County is the central county of the Indianapolis–Carmel–Anderson MSA in Central Indiana.