Here in Michigan you do not need permits to buy or own land, but you will need permits to build upon it. I know when you purchase land, you have to make sure to obtain the title, just to make sure whoever is selling has clear ownership before you take it off their hands. You'll likely need to sign a purchase agreement, and do a deed transfer as well. So there is a process pretty much anywhere you do it.
But, if you're uncertain about your area, it's best to check with your local permitting office.