First-Come, First-Served (Walk-up) is how everyone camped years ago
๐ - all summer long, and it seemed to work. We were never turned away.
Many public campgrounds have this policy nowdays beginning the day after Labor Day and early spring. Many times if you try to reserve a site online, you'll see "not available" on the sites. That doesn't mean the campground is full; that means they are now not accepting reservations. If you see this during the summer that means those sites are for "Walk-up" only. Most national parks and national forests put aside a certain percentage of sites for those without reservations (walk-up).
Someone mentioned "Walk-IN" sites. They are definitely for tenters.
Your best bet is to first call the park to see how full they are. Then try to arrive either Thursday or Friday morning for a weekend spot. Chances are sites from Sunday evening thru Friday morning will be readily available. This is how we get the majority of sites all summer long. We rarely make reservations. Sometimes it's good to be old and retired. You can be flexible.
๐ Good luck!
Full-Timed for 16 Years
.... Back in S&B Again
Traveled 8 yr in a 40' 2004 Newmar Dutch Star Motorhome
& 8 yr in a 33' Travel Supreme 5th Wheel