Here is a list of links I started on another web site.
When we started planning our Alaska trip one of the things we wanted to do was keep camping costs down. To do this I set up a series of bookmarks to get to various camping sources. Here is the list we used.
US recreation links
US forest service state list
Choosing a state brings up the USFS page for that state with a list of national forests or grasslands
Corp of Engineers
Interactive map that will show campground locations by clicking on a state and then a web page for the campground of your choice
NRM Corps Lakes
BUREAU OF LAND MANAGEMENT
A little harder to use but similar to Corp of Engineers. This is by state and then district
BLM - The Bureau of Land Management
US Fish and Wildlife service
Click on a state and bore in. Hard to locate CG's but usually they are free.
Bureau of Reclamation's Recreation
Interactive map, click an icon brings up site details.
This requires a little more boring in but will eventually get you to a
CG web page
US National Park Service
Canadian recreation links
Parks Canada - National Parks of Canada - National Parks of Canada
British Columbia free campgrounds
BC campgrounds, fee, non fee, private and national parks
This is google based, it allows you to select campground type and then scroll/zoom to area of interest. We found this one worked well when used with the BC sites and trails link.
Similar to above but you have to click on each push pin to determine what type of campground it is after selecting camping from the menu on the left.
This one gives current status and a pdf map. It was a little harder to use. I used the map and Google Earth for a better idea of where a given campground was located
This one kind of combines the above you can sort several ways and they have an app also:
Each state also has their own web site.