It is legal in all U.S. States for second cousins to marry. According to Cousin Couples and the book "Clinical Genetics Handbook," there is a very small, if any, chance of genetic defects in second-cousin marriage.
Cousin Couples states that it is legal for first cousins to marry throughout Europe, Canada, Mexico and in 26 U.S. States. However, the United States is the only western country to have restrictions on cousin marriage. Historically it is estimated that 80 percent of all marriages were between first cousins. It is also estimated that all people are related by no more 50th cousins in relation to each other.