Railway
Opened in 1906, the railway features prominently in the village.
The bridge was constructed in 1904 and the line opened on 2nd April 1906. This photo shows the newly constructed bridge:

Station

Adjacent to the bridge was Ilmer Halt, an on-request station where a telephone was used to ask for the next train to stop at the halt. The station was opened 1st April 1929 serving the London and North-Eastern Railway Company. Initially, 1 northboard and 1 southbound train stopped here every morning on weekdays. Ilmer Halt can be seen in this still image taken from a train cab video in 1962. The station closed the following year:


The station was evidently rarely used, as shown in the Parish Council minutes of 1934:
The Clerk was asked to place on the agenda for next meeting, the provision of a Shelter at Ilmer Railway Halt Longwick-cum-Ilmer Parish Council, Monday April 16th 1934
subsequently:
As it was reported that the Passengers travelling from Ilmer Halt only averaged two a week, the Council were of an opinion no good purpose would be served at present by making application to the Railway Co for the provision of a Shelter at the Halt. Longwick-cum-Ilmer Parish Council, Monday July 9th 1934
News Clippings
Highway Committee, Bucks Free Press, Friday 10th May, 1901
Ilmire Footpath.—The Surveyor brought before the Committee the question of diverting a footpath at Ilmire, and produced a plan thereof. Moved by Mr. Lunnon, seconded by Mr. W. Humphreys, and resolved that this Committee recommend that the Council consent to the diversion of the footpath leading from Ilmire to Longwick, so as to avoid crossing the railway as shown on the plan, if the Parish meeting approve thereof.
Bucks Herald, Friday April 5th 1929
Train Service.—The London and North-Eastern Railway Company announce that a new “Halt,” named Ilmer Halt, will be opened between Princes Risborough and Haddenham, as from Monday, 1st April, and the 6.10 a.m. train from Marylebone to Wotton, the 8.15 a.m. from Wotton to Marylebone, on week-days, and the 8.35 a.m. from Marylebone to Calvert, and the 8.22 a.m. from Calvert to Marylebone on Sundays will call at this Station.
Peterborough & Hunts. Standard, April 12, 1929
The L. and N.E.R. announce that, commencing April 1st, a new halt, to be known as Ilmer Halt, will be available for passenger traffic. Ilmer Halt is between Princes Risborough and Haddenham, in Buckinghamshire.
Bucks Free Press, Friday 13th January, 1939
Train Service at Ilmer Halt
Alterations in train services notified by the London and North Eastern Railway to come into operation in February include the following: Great Central section—7.58 p.m. Princes Risborough to Haddenham. “W” note to read—“Calls at Ilmer Halt 8.3 p.m. on notice being given to the guard at Princes Risborough.” 5.35 p.m. Haddenham to Princes Risborough calls unconditionally at Ilmer Halt 5.41 p.m. every weekday. 7.0 p.m. Haddenham to Princes Risborough calls also at Ilmer Halt 7.6 p.m.
Bucks Herald, Friday May 5th 1944
Railway Fatality: Inquest at Longwick-cum-Ilmer
A verdict of misadventure—that death was from shock due to multiple injuries caused by being run into by a train at Ilmer Halt, on the G.W. and L.N.E. Joint Railway, was entered by the Aylesbury District Coroner, Mr. Stanley E. Wilkins, at an inquest he conducted in Ilmer House, Longwick-cum-Ilmer, on Tuesday. The deceased, Thomas Walker (64), of Walnut Tree Lane, Longwick-cum-Ilmer, was found dead at Ilmer Halt on Saturday morning. He was a sub-ganger employed by the railway.
John Thomas Green, of “Glen Lyn,” Mill Lane, Monks Risborough, a ganger and responsible for the “length” between Princes Risborough and Haddenham railway stations, said that the deceased was a lengthman in his gang and acted as sub-ganger. The deceased had been on that length for 38 years and was originally employed by the contractors who built the line. On Saturday he was in his usual state of health. Witness instructed him to examine the length. At about 10 a.m. witness saw him walking on the north side of Ilmer Halt, carrying a hammer and a bag of keys (wooden blocks) in a bag over his shoulder. He was walking on the down “road,” on the outside of the metals and facing oncoming traffic. That was the last time witness saw him alive.
Charles Alfred Huggins, of London, an engineman employed by the G.W.R., stated that on Saturday he drove the 9.10 a.m. train from Paddington to Wolverhampton. After High Wycombe he had a clear run to Princes Risborough and passed through that station at about 65 m.p.h. He sounded his whistle from the distant signal at Princes Risborough south box until he passed the bridge at Princes Risborough station. He was keeping a sharp look-out on the right-hand side of the engine all the way to Haddenham and neither heard anything unusual nor saw anyone on the line. He passed through Ilmer Halt at approximately 10.16 a.m.
Anne Elizabeth Wheelwright, a children's nurse employed by the Ministry of Health at Ilmer House, stated that about 10.20 a.m. on Saturday she went to Ilmer Halt to meet a train. Whilst on the platform she saw what appeared to be a bundle of rags lying at the far end. She walked along the platform and, as she got near, saw that the object was the body of a man. The police were notified.
Dr. Edwards, of Princes Risborough, who examined the body after it had been discovered, said that there was a wound on the right side of the scalp and fractures to the right forearm, shoulder, collar bone, pelvis, lower part of the spine and both hip bones. From the nature of the injuries, he would say they were caused by a very severe impact and that death was likely to be instantaneous. The cause of death was shock due to multiple injuries.
An inquiry was later held by the Great Western and Great Central Joint Railway. Anne Elizabeth Wheelwright, known as Betty, later married Meric Attenborough.