1 Battalion (Ballina): Unit strength on 11 July 1921 was 729 all ranks, and the strength on 1 July 1922 was 196 all ranks. By 1 July 1922 five of the companies of this battalion had been posted to the 6 Battalion and the 7 Battalion of the 2 Brigade (North Mayo). The companies of the 1 Battalion were located as follows: Ballina, Bonniconlon, Knockmore, Rehins, Breaffy, Attymass, and Ballysokeery. By 1 July 1922 the following companies had been posted to the 6th. Battalion: Bonniconlon, Breaffy, and Attymass; and to the 7 Battalion, Knockmore and Rehins.
2 Battalion (Foxford): Unit strength on 11 July 1921 was 467 all ranks, and the strength on 1 July 1922 was 346 all ranks. The companies of the 2 Battalion were located as follows: Foxford, Culmore, Straide, Callow, Shraheen and Attymachugh.
3 Battalion (Ballycastle): Unit strength on 11 July 1921 was 324 all ranks, and the strength on 1 July 1922 was 392 all ranks. The companies of the 3 Battalion were located as follows: Ballycastle, Lacken, Moygownagh, Killala and Kilfian.
4 Battalion (Crossmolina): Unit strength on 11 July 1921 was 605 all ranks, and the strength on 1 July 1922 was 318 all ranks. The companies of the 4 Battalion were located as follows: Crossmolina, Lahardane, Keenagh, Rakestreet, Ardagh and Eskragh. By 1 July 1922 the Ardagh Company had been posted to 7th Battalion.
5 Battalion (Corballa): Unit strength on 11 July 1921 was 363 all ranks, and the strength on 1 July 1922 was 434 all ranks. The companies of the 5 Battalion were located as follows: Castleconnor, Enniscrone, Culleens, Easkey, Dromore West and Corembla.
6 Battalion: Unit strength on 11 July 1921 was 336 all ranks. By 1 July 1922 six of the companies of this battalion had been posted to the 2 Battalion and the 5 Battalion of the 5 Brigade (North West Mayo) 4 Western Division. On 11 July 1921 the companies of the 6 Battalion were located as follows: Doohoma, Dooyork, Doolough, Shraigh, Bangor, Curranboy and Glenamoy. By 1 July 1922 the following companies had been posted to the 2 Bn. 5 Bde.: Doohoma, Dooyork, Doolough, and Bangor; the Curranboy, and Glenamoy companies had been posted to the 5 Bn. 5 Bde and the Doolough company was non-existent.
  – 6 Battalion (Bonniconlon): Unit strength on 1 July 1922 was 257 all ranks. This unit in the formation given below did not exist on the first critical date. On 1 July 1922 the companies of the 6 Battalion were located as follows: Bonniconlon, Attymas, Breaffy and Cloonslane.
7 Battalion (Belmullet): Unit strength on 11 July 1921 was 546 all ranks. By 1 July 1922 seven of the companies of this battalion had been posted to the 1 Battalion and two companies to the 5 Battalion of the 5 Brigade (North West Mayo) 4 Western Division. The locations of these companies will be given below. On 11 July 1921 the companies of the 7 Battalion were located as follows: Belmullet, Barahane, Corclough, Binghamstown, Tirrane, Carramore, Gortmelia, Pullathomas, and Foxpoint. By 1 July 1922 the following companies had been posted to the 1 Bn. 5 Bde: Belmullet, Barahane, Corclough, Binghamstown, Tirrane, Carramore, Foxpoint and the Gortmelia, and Pullathomas companies had been posted to the 5 Bn. 5 Bde.
  – 7 Battalion (Rehins): Unit strength on 1 July 1922 was 209 all ranks. This unit in the formation given below did not exist on the first critical date. On 1 July 1922 the companies of the 7 Battalion were located as follows: Rehins, Knockmore, Ardagh, and Tullysliva.

Active Service Unit: There were two A.S.U’s effective with the 2 Brigade (North Mayo) on 11 July 1921. The No. 1 A.S.U. had a strength of 37 all ranks, and the No. 2 A.S.U. had a strength of 43 all ranks. Personnel were attached to the A.S.U. from the battalions of the brigade and the file contains listings of persons concerned.