What is this berry?
I'm not entirely sure from these photos, but I'm learning toward Glossy Buckthorn.
I assume it's not something that was planted intentionally?
Are you able to take another look at it?
This publication gives a good picture of how I'm able to ID buckthorn--the "thorns" on the ends of new shoots: http://hort.uconn.edu/detail.php?pid=392
if you can see those, then we know it's buckthorn, which is an invasive.
if you don't see those, can you send an additional photo or two of the branches, close up as well as some info on how tall this is and where you've found it? It looks like it's in the woods. Is it damp where it is or pretty dry, does it get sun or not much?
Assuming it IS buckthorn, you should know it's an invasive species and if practical, should be removed. This publication from the DNR is very good: http://files.dnr.state.mn.us/natural_resources/invasives/terrestrialplants/woodyplants/buckthorn_wha...
Another Master Gardener suggested: Alternate Leaved Dogwood. Cornus alternifolia is the scientific name.