New Yorkers have been on line since before there was online—for nearly a century, at least.
They are so prominently on line, in fact, that those of us in the hinterland know it’s a way to identify New Yorkers by the way they talk. Not by their pronunciation, but by their words. If instead of waiting in line or standing in line, you wait or stand on line, you must be from New York—the city, that is, and neighboring New Jersey.
That fact is confirmed by the recent Dictionary of American Regional English. The entry for on line in Volume 3 identifies New York City and northern New Jersey as the area where people say they’re waiting or standing on line.
The earliest evidence in that dictionary is from 1958, but on line wasn’t new even then. Google Ngrams provides published examples of New York on line going back as far as the 1920s. For example, here’s an ad in a 1927…