How the state got this name is actually a very interesting story. The naming of the Green Mountains and the subsequent translation to "Vermont" is detailed in this article by Joseph-Andre Senecal. Here is an excerpt:
Grammatically, the word order (adjective + noun: vert + mont) and the fusion of the adjective and the noun are perfectly correct. In modem French, one would say in a normal enunciation: les monts verts. However the creation of Young is probably not inspired by modern French, even the modern French of 1777. Above all, grammatically speaking, it is not part of a sentence. The word answers the special rules of geographical naming.