Do most state parks have a 30-foot length limit?

Obviously, every park will be different. A park recently built in an open area may be able to accommodate any size rig, while an older park built in the mountains may have size restrictions. There is no one size fits all, but a 30 foot rig should fit in many state and federal campgrounds.

Your home state does not.

Not in Montana. Actually, it varies by park. I do not believe there is, nor can there be, any flat answer to a question like that.
I take our 32 foot Class A to many parks around here, no problem.
A 36 footer may have trouble in some spaces, and a 40 footer or larger might not fit at all. However, there is often at least one space where a big rig will fit. It is often first come, first served, though, so it may have a tent or a truck camper in it when you arrive.
Good luck.

This site had good information:

http://www.forestcamping.com/dow/list/nflist.htm

Most state parks have multiple sized sites. Availability of larger sites might be less, but a 32 footer, you shouldn't have a problem.

Mike

In more them 30 years we have only see a length limit one time.