The last time I was in an airport in the wee hours of the AM, I was on a TWA redeye in St Louis. I think Ronald Reagan was president, so it's been a while. As a rule, do airports let you spend the night? If you come in at say, midnight, can you just hang around until your 7:00 AM flight? I'm curious because it might impact a milage run I'm planning. I put this question here because I want to know about a number of different airports. Is there any place I could go to get that information?

TIA,
Bill