Just because land is considered public land it doesn't mean that camping on the public land is always allowed.
There are some public use land that can be legally camped on and some you need a permit while other public use lands may not need a camping permit.
Usually if the public use land doesn't permit camping they will usually have a sign posted stating no camping allowed.
But if the public land doesn't have any signs forbidding camping then it's likely okay to camp on the public land.
The worse that could happen would be that a game warden or cop comes by and tells you that you need to leave and will usually warn you.
When you do camp on public land you must move to another public land every 14 days unless you have a camping permit that allows you to camp longer.