An Association In Everything But Name?

This question was submitted by Jerry from Illinois

We have an informal condo association — we collect dues, keep records, file taxes, and have bylaws — but we're not registered with the state, and there's no mention of the association in property deeds.

We want to know how to form and register a legal association as for now we have no recourse if someone doesn't adhere to the established rules. How do we start?