Are you sure it had samaras? Looks like sugarberry (Celtis laevigata) which has small, hard berries.

I agree, looks like Celtis.

I believe you are right. The samara groups probably blow over from a neighboring tree; lots and lots are found under this tree. But I have also found these berries on the ground, which I thought dropped from my neighbors tree across a small creek between our yards. Are these sugarberries?

Here's what confused me: I only find the berries to one side of the tree, while bunches of these samara are found under and around it. Also, a number of box elder bugs usually make an annual appearance in the garden beneath. I think it's a case of misplaced features from other trees, and you both are right about it being a sugarberry. Thank you both!

Now please keep an eye out for my next mysterious entry, which also has berries, but they are still green on the branches. I really have tried to research these on my own, but to no avail.