The Belfast & County Down Railway Company was incorporated on 26th June 1846 and continued in operation until it was subsumed into the Ulster Transport Authority (UTA) in September 1948. At its peak it controlled eighty miles of line. The first section of line that was constructed was between Belfast and Holywood and it saw its first passengers on 2nd August 1848. Ultimately this line extended to Bangor. The railway's main line ran from Belfast to Newcastle. There were also branch lines to Ardglass, Ballynahinch and Ardglass. At one stage the Company operated a paddle steamer as well as buses.
The Belfast Holywood & Bangor Railway Company (BHB) was established in 1865. The Belfast & County Down Railway Company was experiencing financial pressures and as a consequence sold the Belfast - Holywood line to the BHB. However it was not long before the BHB also started to experience financial problems and in 1884 as a consequence of an Act of Parliament all the assets of the BHB were transferred to the Belfast & County Down Railway Company. The Debenture stock reflected in the certificate pictured here was issued consequent upon the 1884 Act. The Stock was charged upon the assets of the then defunct BHB.