[x]

Marital rape was a term that was viewed by the law as an oxymoron until shamefully late in U.S. history. Until the 1970’s, the rape laws in every state in the union included an exception if the rapist and the victim were husband and wife. In 1993, all 50 states had finally eliminated the “marital rape exception.” Source

It is also a defense to a charge of first or third degree sexual assault against a child age 14 or 15 that the defendant and the child are married. This is a remnant of the marital rape exemption, which has otherwise been abolished in Hawaii. (Haw. Rev. Stat. §§ 707-730, 707-732.) Source

[jonrick46]

If the marriage was a polygamous marriage, that was in violation of the law and, of course, does not count. He would have been convicted, because the polygamous marriage did not solve the problem.