Ohio is not one of the US states that forms the demarcation line of the Mason-Dixon line.

The Mason-Dixon line, also called the Mason and Dixon line or Mason's and Dixon's line, is a demarcation line separating four U.S. states, forming part of the borders of Pennsylvania, Maryland, Delaware, and West Virginia (part of Virginia until 1863). Historically, it came to be seen as demarcating the North from the South in the U.S.

It was surveyed between 1763 and 1767 by Charles Mason and Jeremiah Dixon in the resolution of a border dispute involving Maryland, Pennsylvania, and Delaware in Colonial America. The dispute had its origins almost a century earlier in the somewhat confusing proprietary grants by King Charles I to Lord Baltimore (Maryland) and by King Charles II to William Penn (Pennsylvania and Delaware).

Charles Mason (April 1728 – 25 October 1786) was an English astronomer who made significant contributions to 18th-century science and American history and Jeremiah Dixon (27 July 1733 – 22 January 1779) who was an English surveyor, are best known for their work from 1763 to 1767, in determining what was later called the Mason–Dixon line.

More Info: en.wikipedia.org