Summit County is an urban county located in the northeast region of the U.S. state of Ohio. As of the 2020 census, the population was 540,428, making it the fourth-most populous county in Ohio. Its county seat and largest city is Akron. The county was formed on March 3, 1840, from portions of Medina, Portage and Stark counties. It was named Summ…Summit County is an urban county located in the northeast region of the U.S. state of Ohio. As of the 2020 census, the population was 540,428, making it the fourth-most populous county in Ohio. Its county seat and largest city is Akron. The county was formed on March 3, 1840, from portions of Medina, Portage and Stark counties. It was named Summit County because the highest elevation on the Ohio and Erie Canal is in the county.