The 4 arrondissements of the Ain department are:[1]
- Arrondissement of Belley, (subprefecture: Belley) with 104 communes. The population of the arrondissement was 124,868 in 2021.
- Arrondissement of Bourg-en-Bresse, (prefecture of the Ain department: Bourg-en-Bresse) with 199 communes. The population of the arrondissement was 342,454 in 2021.
- Arrondissement of Gex, (subprefecture: Gex) with 27 communes. The population of the arrondissement was 102,027 in 2021.
- Arrondissement of Nantua, (subprefecture: Nantua) with 62 communes. The population of the arrondissement was 93,853 in 2021.