As many of the mines and factories closed in the late 20th century due to restructuring, there was a loss of jobs and population.

Saint-Chamond was originally a fort guarding one of five aqueducts that supplied the Roman city of Lugdunum (Lyon).

A number of older buildings survive, including House of Canons of the 15th and 16th sixteenth centuries (listed building), Hôtel-Dieu (historical monument); St. Peter's church from the 17th century, with 19th-century organs by Claude-Ignace Callinet (historical monument); and the 17th-century convent of the Minimes, now the town hall of Saint-Chamond.

The Convention sent Claude Javogues to the city, who imposed fines and summary executions to suppress unrest.

Saint-Chamond is the largest town in the Vallée du Gier metropolitan area and the third-largest population center in the Loire department, after Saint-Étienne and Roanne.

The population data in the table and graph below refer to the commune of Saint-Chamond proper, in its geography at the given years.

[5] Starting in 1771 the Neyrand brothers had become owners of several coal mines and ironworks in the valley of the Gier river.

[7] The community became a center of a region of coal and iron production in the 19th and 20th centuries, stimulating its industrialization and growth.

[9] Later they introduced innovations such as a mobile crane for moving large pieces around the works, and a hydraulic press.

[10] The company of Neyrand frères et Thiollière was formed in January 1845 to exploit an enlarged and modernized factory at Lorette.

During World War I (1914-1918) the steel company built several different types of weapons, notably the Saint Chamond-Mondragón 75 mm gun, which had been designed mostly by colonel Rimailho, the Saint-Chamond tank, and the Chauchat machine rifle.