La Ferté-Alais (French pronunciation: [la fɛʁte alɛ] ⓘ) is a commune in the Essonne department in Île-de-France in northern France.

It used to be a fortress closing the access to the French royal estate from the Essonne valley, then became an industrial village with sand and stones.

Its airfield (actually in Cerny), hosts a world-famous air show for vintage World War I and WWII aircraft and a museum of such aircraft.

It even has the aircraft (still airworthy) that Louis Blériot used to cross the English Channel in 1909.

The name La Ferte-Aleps appears in the Cassini maps and the final name of the commune is registered during its creation in 1793.