The term is thought to have been coined in New York City, where it was in use by the 1830s to refer to the original town at the southern tip of the island of Manhattan. As the town of New York grew into a city, the only direction it could grow on the island was toward the north, proceeding upriver from the original settlement (the "up" and "down" terminology in turn came from the customary map design in which up was north and down was south). Thus, anything north of the original town became known as "uptown", while the original town (which was also New York's only major center of business at the time) became known as "downtown".
During the late 19th century, the term was gradually adopted by cities across the United States and Canada to refer to the historical core of the city (which was most often the same as the commercial heart of the city).
Uptown is a residential part of town away from the central commercial district. The word uptown originated in the New York city train stations. As you leave downtown Manhattan the trains direct you to Uptown. Uptown includes Harlem, East Harlem, Washinton Heights, Inwood and (sometimes) the South Bronx.