I also got a list by distance. But it had to be typed in as "Springfield, IL USA"...
For me, the easiest way to find campgrounds in unfamiliar areas is to use the Allstays app and type in the desired city or town.
Various camping venue types (even Walmart) are identified by symbols on a map, and you can keep moving/enlarging/shrinking the map to see other options further away in different directions. When you click on a symbol, it brings up a short summary window and if desired you can click on the Reserve America website from there.
Allstays Camp & RVI used to Google "RV Park (town name)", but got all kinds of unrelated businesses.
Another nice thing about Allstays is the built-in GPS so if it's time to call it a day, you can see nearby camping wherever you happen to be at the moment (even if you don't know the name of your closest town.)
We use it on the ipad (with 3G internet) to plan trips and to find places while driving down the highway.
