The first portion of the Belfast & County Down Railway to be opened was that along the shore of Belfast Lough, from Belfast to Holywood, which was opened for traffic on 2nd August, 1848.  At that time the main line, which was to run through the suburbs of Ballymacarrett, Bloomfield, Neill’s Hill, and Knock, had been constructed as far as Dundonald.   This line was continued to Comber, where it swung northwards towards Newtownards, and this entire section was opened on 6th May, 1850.

The main line beyond Comber was much more difficult to construct because of the numerous rock cuttings required, and it was not until 10th September, 1858 that the line from Comber to Ballygowan, Saintfield, and Ballynahinch was officially opened, with services commencing on the following Monday, 13th September.  Meanwhile, construction had commenced at Downpatrick, and the connection with the operational part of the system was made at Ballynahinch Junction in the early part of 1859, the line being opened for traffic on 23rd March, 1859.

The Newtownards line was later extended to Donaghadee, with the first trains running into Donaghadee on 3rd June, 1861.    The line from Holywood to Bangor was opened in May, 1865 by the Belfast, Holywood & Bangor Railway Company, who in the meantime had purchased the Belfast – Holywood portion from the B.& C.D.R.    The entire Belfast – Bangor line reverted to B.& C.D.R. ownership in 1884.

Construction of the main line from Downpatrick to Newcastle was undertaken by the Downpatrick, Dundrum & Newcastle Railway Company, and was opened on 25th March, 1869.   The D.D.& N.R. was associated with the B.& C.D.R. through directors common to both boards, and from the beginning was worked by the parent company, being eventually purchased outright in 1891.

The Downpatrick, Killough & Ardglass Railway was incorporated in 1890 by the B.& C.D.R., who were also to operate and maintain it.   Construction was aided by government grants, and it was opened for fish traffic on 31st May, 1892, the first passengers being carried on 8th July. Simultaneously a loop line was built across the Quoile Marshes outside Downpatrick, enabling trains to run through between Belfast and Newcastle, without the necessity of engines having to run round their trains at Downpatrick.

The last section of the B.& C.D.R. to be built was an extension from Newcastle to Castlewellan, which was opened on 24th March, 1906.   This line was of no use what-so-ever to the B.& C.D.R., but was built in self-defense in an attempt to prevent the Great Northern Railway from gaining access to Newcastle.   In the end the government granted the G.N.R.(I) running powers over the ‘County Down line into Newcastle, whilst the B.& C.D.R. were given running powers, which they never exercised, over the G.N.R.(I) tracks to Ballyroney.

In the early 1900′s the B.& C.D.R. was one of the most prosperous railways in the whole of Ireland, when for a period of over 20 years the dividend on ordinary shares stood at 6½%.   Like all other railways in Ireland however, the ‘County Down was to suffer from the development of road transport.    In the years between the two World Wars the situation became desperate, and the intervention of the government was sought by all the railway companies in an attempt to beat off the challenge of the road transport operators.   The government’s answer was Nationalisation!

As a result of the government’s intervention, the Ulster Transport Authority came into being on 2nd September, 1948.   The new Authority was to absorb the Northern Ireland Road Transport Board; the L.M.S.- N.C.C.; and the B.& C.D.R.   The independent existence of the B.& C.D.R. therefore came to an end at midnight on 30th September, 1948 when it was merged with the N.I.R.T.B., and within a few months the U.T.A. announced its intention to close most of the rail system.

On 15th January, 1950, the main line from Comber to Newcastle, along with the branches to Ballynahinch and Ardglass, were closed to traffic.   On 22nd April, 1950 the main line between Ballymacarrett Junction and Comber, along with the branch from Comber to Donaghadee, was closed.   The tracks were eventually lifted following the passing of an ‘Abandonment Order’ by the Stormont government in June 1953.

The Newcastle – Castlewellan line remained open until the G.N.R.(I) line was closed on 2nd May, 1955, leaving the Belfast – Bangor branch, now operated by Northern Ireland Railways, as the sole surviving portion of a once prosperous system.