If you have lived in California for more than 6 months, California is your children's home state, oer the UCCJA.
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There is a concept in the law called "convenient forum" which will often determine where a case should be heard. There is a strong likelihood that after six months, if the children live in another State, and no one has a significant contact with Illinois, the State where the children reside is most likely to be considered the "home State". Depending upon the facts of a case, and if no one objects, then there is a slim possibility that a dispute could be heard in Illinois. At some point, the judge in Illinois will ask, "Why is this case still here if no one lives here anymore?" That will be the crucial question, I think.
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Illinois should decline to retain jurisdiction at this point, since you, your husband, and the children no longer reside in the state and have not done so for 6 months. I would question why you want Illinois to retain jurisdiction? If you or your ex-husband are considering filing any motions, or requesting modification of any orders, then you will likely have to retain attorneys and personally appear in court, therefore it is probably easiest for California to take jurisdiction now anyway.