215 ILCS 5/221.3
In any delinquency proceeding begun in this state against a domiciliary insurer of this state, claimants residing in a reciprocal ancillary state may file claims either with the ancillary receiver, if any, 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 proceedings.
In any such proceeding controverted claims belonging to claimants residing in ancillary states may either (a) be proved in this state as provided by law, or (b) if ancillary proceedings have been commenced in such ancillary state, may be proved in such ancillary proceedings. In the event a claimant elects to prove his claim in ancillary proceedings, and, if notice of the claim and opportunity to appear and be heard is afforded the domiciliary receiver of this state, such claim, when allowed by the court in the ancillary state, shall be accepted in this state as final and conclusive as to its amount, and shall also be accepted as final and conclusive as to its priority, if any, as against special deposits or other security located within the ancillary state.
215 ILCS 5/221.3