In Illinois you have to live together 7 years for common law marriage. But I thought that these days, you don't even need to get married in order to get things like health insurance from your "significant other"
Illinois does NOT allow common law marriages to be formed in their states. Here are the states where common law marriages can be formed.
Alabama
Colorado
Iowa
Kansas
Montana
New Hampshire (only for inheritance purposes)
Oklahoma? (There is apparently conflicting case law as to whether it has been abolished)
Rhode Island
South Carolina
Texas
Utah
Washington, D.C.
In a few states- common law marriages were only recently abolished, so those formed before that date are still valid:
Georgia (before 1/1/97)
Idaho (before 1/1/96)
Ohio (before 10/10/91)
Oklahoma (if abolished, then before 11/1/98)
Pennsylvania (before 1/1/05)
Common law marriage formed in any of this states are recognized in every state, so if you form a CLM in Iowa and then move to Illinois and split up, you must get a divorce in order to remarry. There is no time limit- you can live together and hold yourself out to be married for two years and be married, and you can live together and get things separate for twenty years and not be married.