There are no native snakes in Ohio with diamond-shaped markings. A lot of people don't know the difference between "diamond" shapes and square or rectangle shapes, though, and because people know of the existence of Diamondback Rattlesnakes(which are NOT found in Ohio), they automatically call every snake pattern a "diamond" pattern. If you could provide a few more details, I could probably help you. Google is a great help though; here's a site on Ohio's native reptiles: www.dnr.state.oh.us . You can click on the names of the snakes found in that state, and it will show a photo of the snake and a description, so you see which one most closely matches the snake you're trying to describe.
The diamondback rattle snake has diamond patterns on it's back but it is not found in Ohio. .