Central? Metro Denver or East?
There is plenty of public land in the western, mountainous portion of the state. It's not that difficult to find free camping places if you are away from the more popular tourist destinations of the mountains. There is a lot of private land within Forest Service boundaries however, so good map resources are necessary.
It can be a lot harder to find these free campsites the closer you get to metro Denver. Much easier the farther you get away from metro Denver. Good luck.
If you were to ask about a specific area of the state, perhaps a few of us could help you.