 Into the early 20th century, the population was concentrated in two areas, one at Manassas (site of a major railroad junction), and the other near Occoquan and Woodbridge along the Potomac River, which was an important transportation route.Beginning in the late 1930s, suburban residential development began and new housing was developed near the existing population centers, particularly in Manassas.In 1960 the population was 50,164.