While it's true that the traveler must comply with any state laws for the state in which they're entering, generally speaking, US Customs will not enforce state laws, and only care about the federal duty limits on alcohol. With the one exception being...
Originally Posted by
cagalindo
My sister brought 2 large bottles in her checked bag. No problem at all.. shes not even 21.. She never declared anything..
... that no importation is allowed for travelers under 21, since the drinking age in all states is 21. As to the above situation, it's the same as the Cuban cigar situation: it's called smuggling. I don't think the OP was asking about how easy it would be to smuggle undeclared goods in through Customs without getting caught, but rather was asking on what the duty-free allowance was.