First cousins can legally marry in Tennessee. Found this out because a couple I know went to prenatal counseling and were asked whether they were first cousins. Dr. said it was a standard question because if they were the risks of genetic anomaly we're higher. True story.
http://www.ncsl.org/research/human-services/state-laws-regarding-marriages-between-first-cousi.aspx
According to NCSL, first cousins can legally marry in AL, AK, CA, CO, CT, DC, FL, GA, HI, MD, MA, NJ, NM, NY, NC*, RI, SC, TN, VT, and VA. Allowed under certain circumstances in AZ, IL, IN, ME, UT, and WI.
First cousin marriage is allowed in these states under the following circumstances:
Arizona- if both are 65 or older, or one is unable to reproduce.
Illinois- if both are 50 or older, or one is unable to reproduce.
Indiana- if both are at least 65.
Maine- if couple obtains a physician's certificate of genetic counseling.
Utah- if both are 65 or older, or if both are 55 or older and one is unable to reproduce.
Wisconsin- if the woman is 55 or older, or one is unable to reproduce.
*
North Carolina- First cousin marriage is legal. Double cousin marriage is prohibited
Allowed in a lot more states than I thought it would be.