Source: Pathfinder RPG Core Rulebook, pg(s). 24
Half-elves originally were the results of interracial human-elf relationships but have developed into a true-breeding race since then. They combine human and elven traits, and due to the fact that both races see too much of the other in the half-elf, they are usually never truly welcome in either society. On the other hand, the combination of human skill with elven beauty makes them good artists and entertainers as well as well-traveled adventurers.
Half-elves stand taller than humans, yet shorter than elves. They retain the lean build and comely appearance of the elves, though their ears are less pronounced. Their skin, while fair, takes its color from their human lineage.
Half-elves in Golarion
While large parts of Golarion are unknown, so far it is safe to assume that half-elves live everywhere where their parent races co-exist. Follow the links for more information about half-elves in the respective region.