In most places in the US, it's not trespassing if you camp on private land, provided:
1. There's no "no trespassing" sign posted
2. The land is unimproved (no buildings, fences, lots, etc)
3. You do no damage to the area (littering, brush clearing, campfire, etc)
4. No one tells you to leave.
If the property owner finds you and tells you to leave, you then must leave. But as long as you do so quickly, you still haven't trespassed or broken any laws. This type of trespassing law is a godsend for roadside campers.
Last edited by alpacalypse; 08-04-11 at 06:13 PM.
Reason: Forgot the bit about damaging the campsite