Harlem isn't rural...
People leaving dog food out for their dogs and feeding feral cats or having food in the kitchen and a pet door , or not tying down their trash can lids... coons figure out how to get those goodies real quick. There’s more coons in cities than you’ll see in the woods.
The Bronx parks and queens parks have plenty. It seems raccoons take trips on open bed and not secured box trucks with good eats in them. Also during the wee hours the bridges are safer to negotiate for the little buggers
All it would take is two, and perhaps five years' worth of breeding in abandoned buildings etc. Precisely because Harlem isn't rural, they would have no natural enemies.
They're coming from Central Park and have probably always been around.
West Harlem is currently undergoing a rapid gentrification. Wealthy whites are moving in and displacing the minorities who have made Harlem their home for generations. They're building upscale restaurants and shopping areas, sending rents through the roof and, apparently, complaining about the raccoons.
They are native to the parks and are probably overflowing their habitat.