^ I was just trying to figure this out.
The land area they are talking about is about 5 sq miles. 5 sq miles = about 13 sq km, and St.John's overall population density is listed at about 225 per sq km, but that includes lots of vacant land. Using that figure it would be only 2,925, but in reality the density would be much higher. At typical suburban densities you might have only about 15 to 20 persons per acre. 13 sq km = 3212 acres, and that might mean over 48,000 people to over 68,000, (comparable to or more than the city of Mt.Pearl, CBS and Paradise.
The area of Mt. Pearl is listed at 6.1 sq miles, but that also includes undeveloped land.
http://en.wikipedia.org/wiki/Mount_Pearl
^ Edit - did some error managment recalculation on this, which raised the figures considerably.