For how long are state and federal aircraft registrations valid? How long is a state registration valid for and how long is a federal registration valid for?
and for state I mean North Dakota if any of you know where to look for that.
Federal registration is for three years, according to the FAA (the actual regulations are in 14 CFR 47.40):


  
  Aircraft registration issued due to renewal expires three years from the expiration date of the previous certificate.
  Aircraft registration issued to a new, import, or reinstated aircraft entering or re-entering the U.S. Civil Aircraft Register
  expires three years after the last day of the month in which it is
  issued.
  


State registration - if any - is up to each state so you need to check with the state where the aircraft's owner registered it.