Lagnieu (French pronunciation: [laɲø]; Arpitan: Lagniœ) is a commune in the Ain department in eastern France.

Attached to the foothills of southern Jura (Bugey), it belongs to the natural region of the plain of Ain, also name of the industrial park established about ten kilometers west of the town.

[3] Around 1430, the inhabitants of Lagnieu seized six oxen belonging to the monks of the Carthusian monastery of Portes and ravaged their crops by releasing their pigs.

[5] In 1957, during the passage of a metal element intended for the Marcoule nuclear power plant, the "centipede", the Lagnieu fountain was accidentally destroyed.

Several natural disasters have occurred in the past such as floods and mudslides (April 30 and May 1, 1983, September 26, 1987, October 9 to 12, 1988, February 13 to 18, 1990, June 25, 2006 Lagnieu, like the Lyon region, is located at a climatic crossroads.