U.S. State Laws Explained

 
Second cousins may legally marry All States
First cousins may legally marry AK, AL, CA, CO, CT, FL, GA, HI, MD, MA, NJ, NM, NY, NC, RI, SC, TN, TX, VT, VA 
and Washington DC
First cousins and first cousins once removed cousins prohibited AR, DE, IA, ID, KS, LA, NH, MI, MN, MO, MS, MT, ND, NE, OR, OK, PA,  SD, WV, WY
IN, KY, NV, OH, WA, WI
First cousins and first cousins once removed  prohibited only if they can not bear children or are over a certain age AZ, IL, ME, UT,
IN, WI
First cousins may marry if the submit to genetic counselling  ME
Only double first cousins prohibited NC
Cousin marriages allowed only if permitted by aboriginal culture of the couple MN
Cousins may legally evade state laws and marry elsewhere
(Interperetation of law unclear)
(Not legal but Ethridge v. Shaddock may have set a precedent to overturn)
IN*, KS, LA, NE, OK, WA, WV, WY, 
MI
AR**
Cousins are prohibited from marrying, but are not defined as incest 
(defined as incest only if over 18)
(defined as incest only if under 18)
ID, LA, MN, MO, MT, OR, PA, WA, WV, WY
AZ
SD, 
Cousin marriage is defined as incestuous only if couple is of reproductive age or ability WI
Cousin marriage is defined as incestuous All prohibited states, excluding those listed in the previous two (2) categories
Half-cousins can marry (absolute, apparent) NE, NV
AZ, KS, MT, OK
Adopted cousins may marry with proof of eligibility LA, MS, OR, WV, 
Uncle/Niece and other consanguineous marriages allowed i permitted by aboriginal culture  CO, MN
Uncle-in-law/Niece-in-law marriages allowed CT 

* Indiana
While most marriages are void if contracted elsewhere to evade Indiana's law, cousin marriages do not fall under the statute which would make it void:
 

IC 31-11-8-6
Sec. 6. A marriage is void if the parties to the marriage:
  1. are residents of Indiana;
  2. had their marriage solemnized in another state with the intent to:  (A) evade IC 31-11-4-4 or IC 31-11-4-11 (or IC 31-7-3-3 or IC 31-7-3-10 before their repeal); and (B) subsequently return to Indiana and reside in Indiana; and
  3. without having established residence in another state in good faith, return to Indiana and reside in Indiana after the marriage is solemnized.
Cousin marriage is defined under IC 31-11-1-2 section 2.
** Arkansas:
§ 9-11-107. Validity of foreign marriages.

 (a)  All marriages contracted outside this state which would be valid by the laws of the state or country in  which the marriages were consummated and in which the parties then actually resided shall be valid in all the  courts in this state.

Ethridge v. Shaddock, a case won for validating out of state marriages, does not appear to mandate that the couple actually LIVED in the other state at the time of marriage