Not all states recognize common law marriage and its impact on an estate, according to the Wills, Trusts & Estate Prof Blog in "Why Common Law Couples Need an Estate Plan (New York)."
In most states, the idea of common law marriage has been abolished for a long time. Only a small number of states recognized the concept until recently. However, more some states are now beginning to recognize these marriages again.
The reason behind the renewed recognition is probably because more couples are choosing to live together for long periods of time. They are acting like married couples despite never making it “official” through the process of formally getting married.
By recognizing the existence of a common law marriage, the courts are then able to treat the couple as they saw themselves when it comes to divorcing or settling an estate.
What makes a valid common law marriage varies from state to state.
Normally, if the couple holds itself out to the public as married or tells a government agency that they are married, then a common law marriage exists. For example, if the couple files a joint tax return with the IRS, then the existence of a common law marriage will be recognized in those states that allow them and the couple will be in trouble with the IRS in other states.
If you and your partner are considering common law marriage, it would be wise to consult an estate planning attorney regarding the treatment of common law marriage in your state of residence. Since not all states recognize common law marriages, it is important that you understand you may need an estate plan to protect your common law spouse's interests.
Reference: Wills, Trusts & Estates Prof Blog (Oct. 25, 2017) "Why Common Law Couples Need an Estate Plan (New York)."