Illinois has no prohibitions against the use of conditional lien waivers. In fact, conditional lien waivers are ideal. As they are just as enforceable as their unconditional counterpart, but don't become valid until payment is actually received. Having payment clearly defined is also a useful tool to ensure that the payment is actually cleared and deposited in an account before the waiver becomes valid. The only prohibition Illinois law places on lien waivers is that mechanics lien rights cannot be waived either in the contract itself or prior to performance.
Since Illinois doesn't regulate the actual form of lien waivers, it's important to read the waiver carefully. Many times there will be extra provisions included that may end up waiving more rights than anticipated, or agreeing to indemnification. See: Should I Sign that Lien Waiver?
Here are some other resources about lien waiver you may find useful:
NOTE. The information presented here is for informational purposes only. It is not legal advice and should not be construed nor relied upon as such. Furthermore, this posting does not create an attorney-client relationship. If you need legal advice, seek the counsel of a licensed, local attorney.See More...See More...