It approximately corresponds to the historical region of the Pays de Gex.

[3] The communes of the arrondissement of Gex, and their INSEE codes, are:[2] The arrondissement of Gex was created in 1800, disbanded in 1926 and restored in 1933.

[5] As a result of the reorganisation of the cantons of France which came into effect in 2015, the borders of the cantons are no longer related to the borders of the arrondissements.

It is notable for the fact that it changed hands between Switzerland, the Duchy of Savoy and France several times.

The final decision about its political affiliation was made by the Treaty of Paris (1815), which split it between France and Switzerland.