What is the name of this plant I found in a park?
I think this is Lysichiton americanus,  skunk cabbage. It has these large, rolled-up leaves and grows in wet habitats as you describe. In Europe, it is an invasive species, but in America it is native. I am not 100% sure, because I don't know if there are any similar species in the US.

EDIT
As Anongoodnurse pointed out, I was right to be unsure. This is Eastern skunk cabbage, Symplocarpus foetides. This species occurs in the Eastern parts of the USA.