Happy New Year, everyone!

I will be traveling with Choco from Philly to Boston in about 2 weeks.
Since it's much cheaper to purchase an extra seat for Chocho than carrying him on as a pet, the US Airways has booked an extra seat under my name for Choco.
They also informed me that the airline does not require any vet certificate for traveling unless he's a service dog. However, they told me that each state may require a health certificate for traveling.
I've been to the USDA Animal and Plant Health Inspection Service website, but I couldn't find the information for PA or MA.
Does anyone have any experience or knowledge in this matter?
Thank you and happy holidays!