In 1800 the arrondissements of Belley, Bourg-en-Bresse, Nantua and Trévoux were created. In 1815 the arrondissement of Gex was created. The arrondissements of Gex and Trévoux were disbanded in 1926. The arrondissement of Gex was restored in 1933.[2]
The borders of the arrondissements of Ain were modified in January 2017:[3]
one commune from the arrondissement of Belley to the arrondissement of Nantua
12 communes from the arrondissement of Bourg-en-Bresse to the arrondissement of Belley
four communes from the arrondissement of Bourg-en-Bresse to the arrondissement of Nantua
two communes from the arrondissement of Gex to the arrondissement of Nantua
one commune from the arrondissement of Nantua to the arrondissement of Belley