At first I thought they might be black squirrels well outside their territory. In the northeast and midwest, black squirrels are somewhat rare and are even a tourist attraction. The photo below is from 2004 when we lived in Virginia.
A friend helped identify these as Rock Squirrels common in this area. Rock Squirrels burrow in the ground instead of nesting in trees. That turned out to be a challenge on this rocky site so they were trying to dig under the shed. No deal. We shut down that option and they found a place to spend the summer among the rocks on the opposite side of the yard.
They enjoyed water from the bowl out by the creek all summer. Those dark coats must have been quite hot out there in the high temps and relentless sun.
We enjoyed watching them all summer, though they are quite shy and never came near the house like the fox squirrels.
They don't seem to be around now, I'd love to see them back next summer.