FreeCampsites.Net Guides You to Wallet-Friendly Outdoor Adventures by Alan Henry:
The weather is beginning to turn warm, which means more of us will take the time to explore the great outdoors, along with the parks and lands set aside for public use. FreeCampsites.net is a simple web service that shows you where you can pitch your tent for free, do a little roughing it, and get away from it all.P
The service is as simple as the name implies. Just head over, type in a specific location where you'd like to go camping, and you'll see campsites in that area. Even though the name is FreeCampsites, the sites are color-coded so you can see free ones, as well as paid campsites and sites that require a pass or a permit in order to set up. The map and all of its data is crowdsourced, so the more people using it, the better the database gets.