ncsl.org 19 states and the District of Columbia first cousins may not marry in so check for yourself some states law ncsl.org prohibit marriage between first cousins getting married to one’s first cousin is illegal first cousins may not marry in State Laws Regarding Marriages Between First Cousins 19 states and the District of Columbia marry your cousin State Laws Regarding Marriages Between First Cousins first cousins may not marry in so check for yourself so check for yourself