I'm assuming you're talking about Montco, Montgomery County
in Pennsylvania, about an hour north of Philly.
Starting from Springfield (Illinois)
, you'd probably be looking at somewhere near Columbus
for a good midway stop. There should be plenty of pet-friendly hotels there like Comfort Suites or La Quinta, or you can find an Airbnb.
Oh, and if you're in Montco, hopefully you have time to visit Valley Forge National Historical Park
or go shopping at King of Prussia
. There are a lot of great fall festivals going on too!