Residency and domicile are two different things. Your client is domiciled in the other state, but IL still considers him a resident. There are many factors that can be used to determine residency, and only one is where the TP lives or spends time. Basically, where has the TP planted his flag so to speak: driver's license, car registration and inspection, voter registration, church, doctors, banking, where the rest of his immediate family lives, where the kids attend school, mailing address, still maintains a home in that state, social club memberships, etc.