GEX, a town of eastern France, chief town of the arrondisse ment of Nantua, in the department of Ain; formerly it was the chief town of the arrondissement of Gex which has since been included in that of Nantua; io m. N.N.W. of Geneva and 3 m. from the Swiss frontier. Pop. (1931) 1,341 town; commune, 2,065. It gives its name to the old Pays de Gex, between Alps and Jura, at various times under Swiss, Genevese and counts of Savoy, until in 16o' it came into the possession of France, retaining, however, until the Revolution its old independent jurisdiction, with Gex as its chief town. The Pays de Gex is isolated by the Jura from the rest of French territory, and until 1926 came with in the circumscription of the Swiss customs, certain restrictions being imposed on its products by the French customs. The town is situated 2,000 ft. above sea-level at the base of the most east erly chain of the Jura.