Cossonay is a municipality in the canton of Vaud in Switzerland. It is part of the district of Morges.

Léman was the name of a canton of the Helvetic Republic from 1798 to 1803, corresponding to the territory of modern Vaud. A former subject territory of Bern, Vaud had been independent for only four months in 1798 as the Lemanic Republic before it was incorporated into the centralist Helvetic Republic. Léman comprised all of the territory of Vaud detached from Bernese occupation, apart from the Avenches and the Payerne which, after 16 October 1802, were annexed by the canton of Fribourg until the Napoleonic Act of Mediation the following year when they were restored to the newly established and newly sovereign canton of Vaud.