Delaware County is a county located in the central portion of the U.S. state of Ohio. As of the 2020 census, the population was 214,124. Its county seat and largest city is Delaware. The county was formed in 1808 from Franklin County, Ohio. Both the county and its seat are named after the Delaware Indian tribe. It is a frequent placeholder on the List of highest-income counties in the United States; Delaware County was listed as the 35th wealthiest county in the United States in 2020.