1808, "country house," from American Spanish rancho "small farm, group of farm huts," from Spanish rancho "small farm, hamlet," earlier "mess-room," originally, "group of people who eat together," from ranchear "to lodge or station," from Old French ranger "install in position," from rang "row, line," from Frankish *hring or some other Germanic source, from Proto-Germanic *hringaz "circle, ring, something curved" (from nasalized form of PIE root *sker- (2) "to turn, bend"). The evolution would seem to be from "group of people who eat together" to "group of people who work and live together." The earlier form of the word in English was rancheria (c. 1600).
The sense of "large stock-farm and herding establishment" is by 1847. In Spanish America, the rancho was a herding operation, distinguished from the hacienda, a cultivated farm or plantation. Meanwhile, back at the ranch as a cliche narration for scene shifts in old Western serials and movies is by 1957.
Ranch-house "principle dwelling house on a ranch" is attested from 1862. By 1947 it was the name given to the modernistic type of low, long homes popular among U.S. suburban builders and buyers after World War II, hence ranch, of houses, "single-story, split-level" (adj.); as a noun, "a modern ranch-style house," by 1952, also rancher (1955); diminutive ranchette is attested by 1948.
Ranch dressing is from 1970, originally in reference to popular Hidden Valley Ranch Salad Dressing Mix, sold by mail order.