The Donegal section started in Ballintra on the T18 and formed a coastal loop through Coolmore on Donegal Bay and back to Ballyshannon. This section included three bridges over the narrow-gauge Co. Donegal Railway, which ran close to the road. This coastal loop is now the R231. After a short section of the T18, the L24 continued east of Ballyshannon to the Co. Fermanagh border near Belleek (later R230 and now R936 and N3) where it joined the then B37 (later A46). This section of the L24 was realigned in the late 1940s, as the building of the Ballyshannon Hydroelectric scheme flooded part of the original alignment. The B37 travelled across Co. Fermanagh through Enniskillen, the northern section became the A46 and the southern section later became the A509.
The Co. Cavan section of the L24
At the border at Aghalane Bridge, the L24 resumed in County Cavan, running through Belturbet to the T10 at Butlersbridge. This is now the N3, a rare example of an L-road becoming a national primary. By the time the Belturbet bypass opened in December 2013, the N3 had been entirely rebuilt from the time of the L24. The bypass section of the former L24 at the Aghalane Bridge became the L5615. The section through Belturbet is now the R197 and the section south of the town is now the L1535.