No, the Harlem World’s Fair did not happen in 1883, nor did it happen at all. But it was proposed in this great illustration from Demarest’s Monthly Magazine, November 1879 (thank you to Harlem Bespoke that originally drew my attention to this image):
The fair would essentially be on the Columbia University land, and stretch from Morningside Park to Riverside Park, and bound on the south side by 110th, and on 125th, on the north.
Note the elevated line entering the frame on the bottom left, on 9th Avenue, then zig zagging to 8th Ave. in the curve of death (a ‘popular’ suicide location before the train was rerouted underground under Central Park West:
In the postcard above, note St.John’s the Devine under the tracks, in the distance – just one arch built.