You can marry a first cousin in Wisconsin, but there are restrictions.
765.03 Who shall not marry; divorced persons.
765.03(1) 
(1) No marriage shall be contracted while either of the parties has a husband or wife living, nor between persons who are nearer of kin than 2nd cousins except that marriage may be contracted between first cousins where the female has attained the age of 55 years or where either party, at the time of application for a marriage license, submits an affidavit signed by a physician stating that either party is permanently sterile. Relationship under this section shall be computed by the rule of the civil law, whether the parties to the marriage are of the half or of the whole blood. A marriage may not be contracted if either party has such want of understanding as renders him or her incapable of assenting to marriage.