If I got married in Mexico is it legal in USA? Never regestered in courts in USA married 6 months in Cancun

If you were married legally there yes, there is nothing to register in the US, if you get married in California, you don't register in TN.

But your had to have a legal marriage in that county, your marriage certificate is the proof you are married. ** and the marriage would have to be a legal marriage in your state, i.e. issues for same sex couples that may not be reconsided in your state in the US