1728, an Englished or otherwise deformed variant of salon (q.v.), and originally meaning the same, "spacious room set apart for reception of company or artistic display."
The specific sense of "large hall in a public place for entertainment or amusement" is from 1747; especially one on a passenger boat (by 1817); it later was used of railway cars furnished as drawing rooms (1842). The sense of "public bar" developed by 1841 in American English. Saloon-keeper "one who keeps a drinking saloon" is by 1839.