Willow Glen continued as an unincorporated community until the 1920s, when the City of San Jose ordered the Southern Pacific Railroad to re-route the Southern Pacific Railroad trunk line which at that time was going down Fourth Street. The Southern Pacific then proposed to re-route down Lincoln Avenue. In order to forestall that attempt, Willow Glen was incorporated as a city in 1927. The railroad was instead re-routed to its current route through a then-unincorporated area now known as North Willow Glen, where its principal user is now Caltrain.