Marriage: Michigan does not recognize "common law" marriage by consent or length of time. MCL 551.2.
Marriage License: For a marriage to be valid, a marriage license must be issued by the county clerk and solemnized before an authorized person. MCL 551.101 and MCL 551.7. A social security number is required for the application, unless exempt under law. 551.102.
Age for Marriage: (1) "An individual who is 18 years of age or older may contract marriage. As proof of age, the individual who intends to be married, in addition to the statement of age in the application, when requested by the county clerk, must submit a birth certificate or other proof of age." MCL 551.103.
Marriage in Another State: "(1) Except as otherwise provided in this act, a marriage contracted between a man and a woman who are residents of this state and who were, at the time of the marriage, legally competent to contract marriage according to the laws of this state, which marriage is solemnized in another state within the United States by a clergyman, magistrate, or other person legally authorized to solemnize marriages within that state, is a valid and binding marriage under the laws of this state to the same effect and extent as if solemnized within this state and according to its laws." MCL 551.271.
Note: Michigan will not recognize an under-age marriage or common law marriage even if it was permissible in another state.
Marriage in a Foreign Country: Michigan will recognize marriages in a foreign county provided that they do not violate the laws and public policy of the State of Michigan (i.e. must be consentual, over the age of 18, with proof of age, and valid license issued).