In how many U.S. states can an adult legally drive without a seat belt?

Except for 1 state, New Hampshire, all states and the District of Columbia require adult front-seat occupants to use seat belts. Adult rear-seat passengers also are covered by the laws in 32 states and the District of Columbia. 34 states and the District of Columbia have primary enforcement. Primary enforcement laws allow a police officer to stop and cite a motorist solely for not using a seat belt. In states with secondary enforcement, police can only enforce the law if the motorist has been pulled over for another violation first.

Source: Insurance Institute for Highway Safety