Liam..
The Railway Gazette quotes the following dates...
The section between Dunboyne and Drumree 8.5 miles was lifted in 1918 and Inny Junction to Longford 15 miles in 1924. The remaining 3.5 miles between Clonsilla and Dunboyne was lifted by 27th July 1926.
The next to go was Galway to Oranmore, 5 miles by 21st September 1926.
Next was Athenry to Attymon, 6 miles by 15th March 1927
( the GSWR singled 23.5 miles between Cherryville Junction and Carlow in 1919, the DSER singled 5 miles between Newcastle and Wicklow by 31st July 1927, and the Cork Blackrock & Passage singled 7 miles from Albert Quay to Blackrock by 12th December 1927, making a total of 73.5 miles by September 1928).
Ballinasloe to Athlone completed by 2nd November 1928, Athlone to Mullingar by 26th May 1929, Mullingar to Enfield by 17th March 1930, Enfield to Clonsilla by 10th August 1030.
18.5 miles between Athlone and Roscommon was singled by November 1930 and 1.5 miles between Ballysodare and Carrignagat also Collooney Jcn and Collooney were singled in the summer of 1930.
Look in the Record Society at Heuston for The Railway Gazette, issues dated 5, 12 and 19th December 1930.
There is an article in the IRRS Journal number 144 February 2001 pages 17-28, Author Oliver Doyle quotes slightly different dates to the Railway Gazette though! ( IRRS Journal no 3 also has coverage)
Michael.