Baltimore's Railroad Partner is the Ohio. The Ohio is a major river in the United States that runs through several states, including Ohio, West Virginia, Pennsylvania, and Maryland. It is the largest tributary of the Mississippi River and is an important transportation route for goods and services. The Ohio River has been used for centuries as a major trade route and was an integral part of the Underground Railroad during the Civil War. Baltimore's Railroad Partner, the Ohio, is an important part of the city's history and economy.