The Thick-billed Euphonia is distributed from Costa Rica in Central America through Colombia and Venezuela to Peru, Bolivia and Brazil south of the Amazon. See the distribution map at Birdlife International. It is replaced further east by the very similar Violaceous Euphonia E. violacea.

In most of its range the male, shown here, is the only euphonia with all yellow underparts. It also has a relatively large yellow patch on the forecrown. Photo 3 shows what I assume to be an immature male.

Most sub-species have white on the underside of the tail but photos 2 and 3 show the sub-species E. l. melanura which has an all black tail.