It's probably Cutlead Geranium, Geranium dissectum, which is an introduced plant from Europe. We find it in lawns sometimes in Wisconsin. It's relatively identical to Carolina Geranium (Geranium carolinianum, a native species), but that one's petals seem wrong to me. Both are found in Pennsylvania.
A good source for you to look at:
Virginia Tech's Weed Identification site (be sure to click the arrows next to the photos on the top of the page to scroll through samples; some will match what you have). This site also gives identifying characteristics that you can use to verify my ID.
Once you've made a tentative ID, an excellent source for determining whether a plant is native or not and where in the US it has been reported is the US Dept of Agriculture's Plant Finder site. You can enter either the scientific name or the common name.