Landing at private sites in the US - restrictions

[birrddog]

Anyone got any pointers as to where I can find restrictions that would govern landing at private sites in the US?

I am trying to find out how one would (ideally online) go about finding restrictions or town ordinances that restrict or govern landing at private sites, e.g. a farm or golf course, etc. (assuming one has land owners permission).

And on a related note, the process and pro's vs. con's of creating a heliport on your own land....

For the latter question I am looking in NY State, the first question more generic across the US.

Thanks in advance