1 West Mayo -Brigade – 4 Western Division

1 Battalion: Unit strength on 11 July 1921 was 677 all ranks, and the strength on 1 July 1922 was 514 all ranks.The companies of the 1st. Battalion were located as follows: Castlebar (No.1), Ballyheane, Islandneady (Islandeady), Glenisland, Crimlin, Ballyvarey, Ballintubber, Burren, Breaghy, and Castlebar (No. 2).
2 Battalion: Unit strength on 11 July 1921 was 964 all ranks, and the strength on 1 July 1922 was 389 all ranks.On 11 July 1921 the companies of the 2 Battalion were located as follows: Kilmeena, Brockagh, Newport, Glenhest, Shramore, Tiernaur, Mallaranny, Ballycarry, Achill, Dooninver, Keel, Cashel, Dooega, Dooagh, Cloughmore and Doohinela.
By 1 July 1922 ten of the companies of this battalion had been posted to the 3 Battalion and the 4 Battalion of the 5 Brigade, 4 Western Division.
By 1 July 1922 the following companies had been posted to the 5 Brigade: Mallaranny, Ballycarry, Achill, Dooniver, Keel, Cashel, Dooega, Dooagh, Cloughmore and Dookinela.
3 Battalion (Westport): Unit strength on 11 July 1921 was 782 all ranks, and the strength on 1 July 1922 was 774 all ranks. The companies of the 3 Battalion were located as follows: Westport, Owenwee, Belclare, Couslough, Derrygorman, Killavalla, Murrisk, Aughagower and Shraheen.
4 Battalion: Unit strength on 11 July 1921 was 487 all ranks. By 1 July 1922 this battalion had been posted as the 2 Battalion, 3 Brigade (West Connemara), 4 Western Division.On 11 July 1921 the companies of the 4 Battalion were located as follows: Louisburgh, Killeen, Achonry, Lecanvey, Culleen and Tully.

Active Service Unit: strength of 185 personnel effective with the 1st. Brigade (West Mayo) Active Service Unit by 11 July 1921, and a strength of 41 personnel effective on 1 July 1922. The personnel were attached to the A.S.U. from the battalions of the brigade and the file contains listings of persons concerned.