Front and eastern side of the Jefferson County Courthouse, located at 301 Market Street in Steubenville, Ohio, United States. Built in 1874, it is part of the Steubenville Commercial Historic District, a historic district that is listed on the National Register of Historic Places. – Nyttend, Public domain – Wikimedia Commons Jefferson County is located in Ohio. About 67,347 people live here. Between 2010 and 2020, the population declined from 69,709 to 65,249. The area covers about 1,064.0 square kilometers. The region is divided into 17 Municipalities. The region was founded in 1797. The name originates from Thomas Jefferson (Founding Father) The license plate code is 41. Jefferson County is county in Ohio, United States. More information at www.jeffersoncountyoh.com.