What kind of plants are nearby?

Maybe the seeds from a fruit some animal is eating...perhaps wild black cherry seeds.

Here is a link that might be useful: Check seeds shown at bottom of page

Certainly a cherry of some sort.

I have two ancient (well, most likely 40- to 55-year-old; no one seems to know when they were planted) cherry trees which bear 1/2", sweet dark fruit. The pits are a scant 1/4".

Decades ago we lived in southwestern CT, surrounded by wild cherry trees. Their pits were a little smaller.

Sizewise, your photo could be either -- with perhaps the edge to a wild cherry tree.

I do have a Cherry tree in my back yard. Didn't know they could be seeds to it because they are in my front yard as well. Birds must be spreading them all over. Thanks for the info.