Here's a site that has butterfly checklists by county
I'm having a pretty hard time trying to ID butterflies I'm seeing in my yard and at some parks near work. I'd used the part of the site below that was for all of NJ and found that pretty helpful. Yesterday somebody on the Butterfly Forum posted a different page of the site. From that page was a choice for checklists that I was very happy to see were by county. At this point narrowing things down will definitely help me. Enjoy.
Here is a link that might be useful: Butterflies of North America, County Checklists