It has a general appearance similar to R. fascicularis, but that one blooms Feb-May and (at least here) typically has leaves with divisions mostly entire. Since yours hasn't yet produced much, if any fruit, and some leaf divisions are sharply toothed, it may be something other than fascicularis.

You're right. The leaves are really throwing me off because they look similar to, but not exactly like, a couple of Ranunculus species. I have always assumed they were buttercup but now I'm not sure.

Consider Ranunculus hispidus, which is common in your area.

The term 'Buttercup' per se doesn't mean much. It's applied to scores of Ranunculus species. So your plant is certainly a Buttercup. It's just a question of which one.