Yes you are if e.g. you're a non-american who is married to a US citizen, or a number of other exceptions to the rule.

And once you land in America (except Hawaii), there aren't any real restrictions on your movement. You can land from a crowded plane, take an uber to the beach, and then go straight to a house party where you lick your grandparents if you so desire. Americans are big on freedoms, rightly or wrongly, which means generally less travel restrictions for those who are here.