Really is town by town- some places count them as temporary structures, we looked into it in our town. They said as long as it wasn't within 200' of a waterway (that is, in a designated Special Resource Area- a legal term for where building restrictions are more, well... restrictive I guess is the best term- look for that language) and it was on a "movable" platform then it would be fine. Don't need to actually be able to move the platform easily, but it should be on skids or wheels with a hitching point. If its considered a 'permanent, immovable structure', then we needed permitting.

That said, getting a permit isn't the end of the world, its not costly and if you just say, I want to put a yurt on my property, they will probably be fine with it. There's no guarantees or absolutes when it comes to small town offices. They might want to you install some sort of outhouse system, but you will want one anyways.