1900 The Royal Electric Company installs an electrical lighting system in the city.
1903 Traffic in Saint-Laurent is regulated. Anyone who violates the speed limit while riding on horseback "faster than an ordinary trot," is fined.
In response to major concerns voiced at the end of the 19th Century, a complete waterworks and sewage system is finally installed to serve the entire city.
1905 The advent of the automobile requires modifications to the traffic laws. The maximum speed limit is set at six miles per hour.
The first volunteer chief firefighter is hired.
1912 Les sœurs de l'Espérance de la Sainte-Famille de Bordeaux arrive in Saint-Laurent and set up a novitiate.
Construction of the first City Hall on de l'Église street. Its location now houses the Municipal Library.
1913 Canada Stoves & Furniture Company Ltd opens an iron stove manufacturing plant in Saint-Laurent.
1914 The Fire Department purchases its first fire truck.
1922 (January) The first hospital of Saint-Laurent officially launches operations.
1925 The Saint-Laurent Police Department acquires its first vehicle.
1929 Robert Mitchell Ltd opens a foundry.
1931 The former St. Andrews and St. James Church of Montréal, taken apart brick by brick the previous year, is reconstructed in Saint-Laurent. It later becomes the Musée d'art de Saint-Laurent.
1937 Continental Can, specializing in the production of tin cans, begins operations in Saint-Laurent.
Brother André dies on January 6 in the hospital of Saint-Laurent.
1939 The arrival of Noorduyn Aviation marks the beginnings of the aerospace industry in Saint-Laurent.
1942 Vickers (later Canadair and today Bombardier Aéronautique) erects a plant for the construction of aircrafts in Saint-Laurent.
The pharmaceutical industry makes its debut in Saint-Laurent with the arrival of Ayerst McKenna & Harrison.
Development of the Norvick District, named after two companies working in the aerospace industry: Noorduyn Aviation Ltd and Vickers.
1946 Saint-Laurent's first permanent firefighter is hired. The City's Police and Fire Department constitutes one chief and six constables.
1947 CAE Électronique manufacturer of flight simulators, open its business in Saint-Laurent.
First city manager, Lucien Toupin is hired.
1950 Norgate Shopping Centre, the first indoor mall in Canada, opens its doors.