I think it's a type of Campanula.

Adenophoro confusa commonly know as 'Lady bells'.
A perfect weed for your woods.
Pondy

I looked this up since I was curious. Appears to be spelled "Adenophora confusa" and I can't find any indication that it is native so it must be introduced. In the google search I did, the link to one site has comments by several people saying it is quite invasive and hard to get rid of once it gets started. Spreads by seed and by runner.

Here's a good post on this plant from the Perennials forum.

Here is a link that might be useful: Lady bells post