I kinda like the local parks that don't take reservations at all. They are a first come first serve basis. They have a 7 day stay limit.
There are a few local parks that take reservations for the year on Jan. 1st. These are also the parks that are mostly seasonal campers. They have like 1 or 2 spots for non-seasonal campers. Those spots are then reserved by the seasonal people. I don't like that fact that these are "public" parks that my taxes go to maintain and then only a few people get to enjoy them.
MN state parks now have same day reservations. The holiday weekends are full. But, any other weekend you have a chance to get in because someone might cancel.
Iowa state parks are 3 months out for reservations. But, only about half of the Iowa camping spots at their parks are reservable. The other half is first some fist serve.
SD state parks are 3 months out for reservations. But, you can cancle up to 2 weeks in advance so if you keep checking you can often find someone who changed their mind and cancelled.
I've never been anywhere else so I don't know how it is done in other places.