I have many camping apps on my iPhone, but find I mostly use Allstay's Camp & RV
and Ultimate Campground Project.
Both are available for either iOS or Android. While both are "paid" apps, they are worth the $. Both have filters that let you only see the type of campground or service you are seeking.
The Ultimate Campground POI list can be purchased for downloading into your GPS.
I also liked CampWhere, still use it at times, but as Raz points out, it is no longer available, and is getting a bit dated.