Legal Question in Wills and Trusts in Illinois

Sorry to hear of your situation. Contrary to the trite phrase, possession is not 9/10 of the law. It is merely possession. Your sister will not have any greater right to ownership simply by living there. Ownership will be determined by your mother's will if she had one. If not, it will go to her spouse and children.

Your sister may have moved in with your mom to take care of her. Your sister may be entitled to compensation for her efforts on your mother's behalf. What happens after your mother dies is governed by the terms of her will. After your mother's death, you are entitled to a copy of the will, either from your sister, or if she's not talking to you for any reason, from the clerk of the court in the county in which your mother resided on the date of her death. A person in possession of a decedent's last will has a duty to file it with the clerk of court within 30 days after the testator's death.