Most people are fuzzy on exactly what common law marriage is. Like so many others, we used to believe that if two people lived together for seven years (or some other magical number of years), clicked their heels three times, and sprinkled some fairy dust, they'd become common law spouses.
That's not exactly how it works.
The idea of common law marriage emerged in medieval England, because clerics and justices who officiated at marriages were not always able to travel to rural locations where some couples lived. In that case, the couple could establish a marriage "by common law."
In most states in the United States** today, there's no such thing as common law marriage. No matter how many years you live together and how much fairy dust you sprinkle, you will never have a common law marriage. That's good news if you're worried about "accidentally" finding yourself married, but bad news if you wanted the perks of marriage without the paperwork. (However, even if you'll never have a common law marriage in the legal sense, this website packed with information for people like you. You might also be interested in Unmarried to Each Other: The Essential Guide to Living Together as Unmarried Couple.)
In fourteen states and the District of Columbia (see below), though, common law marriages are recognized. If a man and a woman (same-sex marriages aren't recognized) live together and "intend to be married" by acting like they are married, telling people they are married, and doing the things married people do (using words like "husband" and "wife," filing joint tax returns, etc.), they become common law spouses. This gives them the same rights and responsibilities as people who got married the old-fashioned way, with a trip to City Hall and a wedding.
Common law marriage isn't something to do lightly. If you become married by common law and later decide you want to end your relationship, you still have to have a standard, legal divorce. In this way, common law marriages are very similar to regular marriages: they're usually easier to get into than to get out of.
There's no simple test to see if a couple qualifies as being common law married, and the only time the question usually arises is in court. If, after death or separation, one partner claims there was a common law marriage and wants the benefits of marriage, the court would consider many factors to determine if there was truly intent to be married. Since the seven-years-to-automatic-marriage idea is only a myth, determining whether a common law marriage existed can be complicated. Some lawyers recommend that couples write, sign, and date a simple statement that says they do or do not intend to be married, to offer protection should the question ever arise.
If you create a common law marriage in one of the states below and later move to a state that does not recognize common law marriage, your marriage can technically still exist. All marriages, common law or otherwise, are recognized by all states, regardless of where they were created (the debate about legalizing same-sex marriage gets tricky here, since technically, a lesbian marriage created in whatever state legalizes it first should be recognized by all other states).
Few of us live in places too rural to be married these days, and fairy dust is scarce. In the U.S. today, common law marriages are more common in myth than in reality.
States That Recognize Common Law Marriage
AlabamaColorado
District of Columbia
Georgia (if created before 1/97)
Idaho (if created before 1/96)
Iowa
Kansas
Montana
New Hampshire (for inheritance purposes only)
Ohio (if created before 10/91)
Oklahoma
Pennsylvania
Rhode Island
South Carolina
Texas
Utah