"one who immigrates," 1792, American English, perhaps based on French immigrant, from Latin immigrantem (nominative immigrans), present participle of immigrare "to remove, go into, move in" (see immigrate). Emigrant is older. First used in English in Jeremy Belknap's history of New Hampshire, and he generally is credited with having coined it.
There is another deviation from the strict letter of the English dictionaries; which is found extremely convenient in our discourses on population. From the verb migro are derived emigrate and IMMIGRATE; with the same propriety as from mergo are derived emerge and IMMERGE. Accordingly the verb IMMIGRATE and the nouns IMMIGRANT and IMMIGRATION are used without scruple in some parts of this volume. [Preface to vol. III of "The History of New Hampshire," Belknap, 1792]
As an adjective from 1805.
1690s, "to pass from one place to another," from Latin migratus, past participle of migrare "to move from one place to another," probably originally *migwros, from PIE *(e)meigw- (source of Greek ameibein "to change"), which is an extended form of root *mei- (1) "to change, go, move" or perhaps a separate root. Of animals, "to remove from one habitat to another at a distance," by 1753. Specifically of persons or groups by 1770, "to pass or remove from one place of residence to another at a distance," especially from one country to another. Related: Migrated; migrating.
To migrate is to change one's abode, especially to a distance or to another country, emphasis being laid upon the change, but not upon the place of departure or that of stopping, and the stay being generally not permanent. Emigrate, to migrate from, views the person as leaving his previous abode and making a new home; immigrate, to migrate into, views him as coming to the new place. The Arab migrates; the European coming to America is an emigrant to those whom he leaves, and an immigrant to the Americans. [Century Dictionary, 1897]