Which state do you register your vehicles in? Which state have you registered to vote in? Which state is your driver's license from? Generally, this are the questions used to establish residency.
I assume this is all where your first home is located. You will continue to file just in that state if that's the case.
The good news is that for federal purposes, you can deduct property taxes (up to $10k limit) and mortgage interest for both your primary and secondary residence.
