215 ILCS 5/221.4
If a delinquency proceeding is commenced in a reciprocal state against an insurer domiciliary in such state, claimants against such insurer who reside within this State may file claims either with the ancillary receiver, if any, appointed in this State or with the domiciliary receiver. All such claims must be filed on or before the last date fixed for the filing of claims in the domiciliary delinquency proceeding.
In any such proceeding controverted claims belonging to claimants residing in this State may either (a) be proved in the domiciliary state as provided by the law of such state, or (b) if ancillary proceedings have been commenced in this State, be proved in such ancillary proceedings. In the event that any such claimant elects to prove his claim in this State, he shall file his claim with the ancillary receiver in the manner provided by the law of this State for the proving of claims against domiciliary insurers, and he shall give, or cause to be given, at least 40 days prior to the date of hearing, notice to the receiver in the domiciliary state, either by mail or otherwise in writing that such claim is being made to such ancillary receiver and the nature and the amount thereof. The domiciliary receiver shall be entitled to appear or to be represented in any proceeding in this State involving the adjudication of the claim. The allowance of the claim by the courts of this State shall be final and conclusive both as to its amount and also as to its priority, if any, against special deposits or other security located within this State.
215 ILCS 5/221.4