The County Donegal Railways Joint Committee operated an extensive 3 ft (914 mm) narrow gauge railway system serving County Donegal, Ireland, from 1906 until 1960. The committee was incorporated by an Act of Parliament in 1906, which authorised the joint purchase of the then Donegal Railway Company by the Great Northern Railway of Ireland and the Midland Railway Northern Counties Committee.
 On 1 May 1906, the Joint Committee was set up. The lines inherited by the Joint Committee totalled 106 miles (171 km) and were:
 By 1912 the company owned the following assets:
 The Strabane to Derry line was completely owned by the Midland Railway Northern Counties Committee, although it was operated by the CDRJC.
 At its greatest extent, the County Donegal Railways Committee operated the largest narrow gauge railway system in the British Isles. The railway was affectionately known as the "Wee Donegal". 
 The Joint Committee opened the Strabane and Letterkenny Railway on 1 January 1909, bringing the total mileage operated by the company to 124.5 miles (200.4 km). Only 91 miles (146 km) were directly owned by the Joint Committee, as the Strabane and Letterkenny Railway accounted for 19.25 miles (30.98 km), and 14.5 miles (23.3 km) were property of the Northern Counties Committee.
 Under the management of Henry Forbes, traffic superintendent from 1910 to 1943, the County Donegal Railways became pioneers in the use of diesel traction. The first diesel railcar was built in 1930 (the first diesel railcar anywhere in the British Isles), although a  petrol-engined railcar had been built in 1926 before standardisation on diesel traction in 1934.  Eight articulated diesel railcars were constructed by Walker Brothers of Wigan between 1934 and 1951, by which time virtually all passenger services were operated by diesel railcar, being much cheaper to operate than conventional steam trains.
 The railcars could only be driven from one end and had to be turned on a turntable to make a return journey. As well, they could not be worked in multiple, so if two railcars were working back to back, both required a driver.  The railcars were incapable of hauling most freight wagons, so steam traction continued to be used on freight and excursion trains. The railcars could haul specially constructed trailers, and some lightweight freight wagons, which were painted red to distinguish them from the heavier wagons, which were grey.  A diesel locomotive named Phoenix (converted from a steam locomotive) was also used, but due to its noisy operation and slow speed (top speed of 27 mph or 43 km/h), it spent most of its career shunting, travelling 204,577 miles (329,235 km) during its working life.
 The Glenties branch closed in 1947, the Strabane-Derry line closed in 1954, and the remaining passenger services ended on 31 December 1959. Much of the railway was closed on that date. Goods trains ran between Strabane and Stranorlar until 6 February 1960.
 During the 1930s the Joint Committee began operating a fleet of buses. After the closure of the railway, it continued to operate as a road freight and bus company until  10 July 1971 when it was taken over by CIÉ.
 In 1961, the two most modern diesel railcars were sold to the Isle of Man Railway.
 Part of the line, which runs alongside Lough Finn near Fintown, has been re-laid as a tourist railway.
 The Donegal Railway Heritage Centre has been established and contains historic details and artefacts of the CDRJC.
 St. Connell's Museum, in Glenties has an extensive display of items from the railway.
 The Foyle Valley Railway in Derry houses numerous CDRJC artefacts. It used to operate a small heritage railway along the Foyle on the original route of the Derry-Portadown railway line, which has since fallen into disrepair during the museum's period of closure.
 UFTM = Ulster Folk & Transport Museum; FVR = Foyle Valley Railway; BHR = Belturbet Heritage Railway; FTR = Fintown Railway; DRC = Donegal Railway Centre; IOMR = Isle of Man Railway; C&L = Cavan and Leitrim Railway
 Scrapped in 1909.
 Scrapped in 1910.
 Scrapped in 1931.
 Scrapped in 1931.
 Scrapped in 1931.
 No. 9
 Scrapped in 1954.
 No. 10
 Scrapped in 1952 after a collision with railcar No. 17 in 1949.
 No. 11
 Scrapped in 1967.
 No. 12
 Withdrawn in 1940, dismantled for spare parts.
 No. 4
 Meenglas
 Preserved at the Foyle Valley Railway Museum.
 No. 5
 Drumboe
 Ran the last scheduled train of the CDRJC on 31 December 1959.
Preserved at the Donegal Railway Heritage Centre.
 No. 6
 Columbkille
 Preserved at the Foyle Valley Railway Museum.
 No. 8
 Foyle
 Scrapped in 1955.
 No. 2
 Preserved in the Ulster Folk and Transport Museums in Cultra.
 No. 3
 Sold at a scrap auction in 1960.
 No. 11 Phœnix was converted from steam power to diesel power and operated as a shunter.
 Preserved at the Ulster Folk and Transport Museums.
 Sold in 1961 and removed to Mountcharles.
 Preserved at the Ulster Folk and Transport Museums in Cultra.
 Scrapped in 1947.
 Sold in 1958 and removed to Inver.
 Scrapped in 1949.
 Phœnix
 Scrapped in 1944.