What states allow juveniles to be executed?

None. The US Supreme Court ruled in Roper v. Simmons, 543 US 551 (2005) that it is unconstitutional to execute an offender for crimes committed while under the age of 18.

This overturned two relatively recent rulings in Thompson v. Oklahoma, 487 US 815 (1988) and Stanford v. Kentucky,492 US 361 (1989) that declared executing someone for capital crimes committed while under the age of 16 was a violation of the Eighth Amendment prohibition against cruel and unusual punishment, but that executing someone who was at least 16 at the time the crime was committed was constitutional.

The decision in Roper v. Simmons, (2005), overturned death penalty laws in 25 states.

The last known execution of a juvenile in the US was 17-year-old Leonard Shockley, who was put to death in 1959.

The last person to be executed for a crime committed as a juvenile was Scott Allen Hain, in 2003.