In Ohio, our squirrel species are called fox, grey, red and flying squirrels. I have seen all of them in my Northeast Ohio area (suburbs of Cleveland), however, the most numerous, by far are the fox squirrels and then followed by the grey. I love squirrels, so forgive me for the mini-wiki that follows, lol!
The Fox Squirrels are the most abundant in my area. They are actually the largest squirrels in North America.The ones in the area are as big as small cats! They are similar to the grey squirrels, except they have orangish cheeks, face, feet and belly. The upper body is yellowish-gray and the fluffy tail resembles a fox tail, it's reddish-orange with a dark hairs sprinkled throughout. There are also some different morphologies possible, but around here we don't see any. At Kent State University I have seen the all black version of this squirrel.
We also have the Eastern Gray Squirrels which look similar to the Fox Squirrels, but are a little smaller and have silvery, white tips on their gray upperparts and a cream underbelly. They are not nearly as fluffy as the Fox Squirrel. (The grey squirrels I saw while at college in Western Mass in the Pioneer Valley, were very grey, not silvery and had no orange on them. They were much more rangy looking, with sparse tails and frankly looked a lot like tree rats to me!)
We also have the American Red Squirrel which is smaller, just a little larger than a chipmunk with very reddish with grey and a cream underside and cream circle around their eyes. They are very aggressive, but adorable and I have only seen them a few times in the area, none where I now live, but they are very territorial and get displaced by the others. They eat primarily pine seeds, so they live in pine trees.
The Southern Flying Squirrels are so stinking cute, but are nocturnal, so many Ohioans don't know we have them. I have watched them raiding the bird feeders at night and they are small about the size of a chipmunk with big dark eyes, lustrous grey-brown upper parts and creamy white underneath. (They remind me a little of chinchillas)
By the way, they don't really fly, they glide, (bats are the only mammal capable of true flight, well, without a machine that is