In 1790, the very first United States Census found that Northern Liberties was the sixth most populous city in all of the United States, weighing in with around 9,900 residents. Granted, the country was pretty small back then, but it made me wonder what caused this Northern Liberties to completely fall off the map.
As it turns out, Northern Liberties was located in present-day Philadelphia, just north of what is now Center City. It was incorporated into the main city boundaries in 1854 and, appropriately, its last appearance on the chart is in 1850. Knowing this, I checked out the "rank of cities" chart for other Philadelphia neighborhoods and found one more, Southwark, coming in at #10 in 1790. Philadelphia itself ranked #2 in the first census, just behind New York City.