Not water hemlock. Take a look at the leave veins coming out from the mid rib. The vein should end in the v-shaped notch along the leaf edge. The veins on these end before they reach the edge of the leaf. I also don't see any of the characteristic red/purple splotches on the stem. I believe that your plant is an elderberry, probably American Black Elderberry, Sambucus canadensis. Here is an article that explains how to tell the difference. It's not a university based article, bu the information is sound, and the comparison is great.
Sambucus canadensis. http://www.eattheweeds.com/ufos-2/look-alikes/elderberry-or-water-hemlock/