Where did the word "hamburger" first appear?

The word “hamburger” first appeared in a Walla Walla newspaper. The earliest widely cited printed use is a reference to “hamburger steak” in the Walla Walla Union of Walla Walla, Washington, in 1889.

The name did not originally mean a sandwich. It came from “Hamburg steak,” a dish of chopped or minced beef associated with German-American cooking and the city of Hamburg. Menus and cookbooks had described Hamburg-style beef before the shorter American term became common.

By the late 19th century, minced-beef patties were increasingly sold by restaurants, lunch counters, and street vendors. Putting the patty between bread made it easier to eat while traveling or working, helping the hamburger develop into the familiar sandwich.

The origin of the dish itself remains disputed, with several American towns claiming to have invented the hamburger sandwich. That is a separate question from the earliest printed appearance of the word, for which the Walla Walla newspaper reference is the standard trivia answer.