The conversion of locomotives from steam power to diesel during the 1950s, as well as highway improvements and increased trucking during the 1960s and 1970s, saw McAdam decline in importance for rail transport.

Original settlement of present-day McAdam area began sometime between 1857 and 1869, after the establishment of the St. Andrews and Quebec Railway (SA&Q).

[5] McAdam began under the name of City Camp which was originally a collective of several lumbering encampments which sprang up alongside the line.

[6] By 1871 McAdam was a junction of limited importance and this contributed to a rise in population to about four hundred people, mostly railroad workers and their families.

Trains often stopped for inspection and servicing at the station and demand for workers caused the population in the town to continue to rise.

In 1915, a German agent, Werner Horn, attempted to destroy the international railroad bridge between Vanceboro, Maine and St. Croix, New Brunswick - immediately west of McAdam - in order to limit the movements of war supplies to the port of Saint John.

New highways constructed after the war saw trucks and automobiles reduce the need for the branch lines to St. Stephen, St. Andrews and Woodstock.

Already suffering from new technological developments and its isolation from any other reliable source of employment, McAdam was devastated after the CPR transferred operation of its passenger service to Via Rail Canada in 1978.

Over the next half-century as the rail operations in McAdam expanded, the population increased substantially: a result of the promise of employment.

More recently, families have been flocking to McAdam looking for a small-town rural home, while also having amenities of the city such as schools, municipal water and sewer, and also all essential shopping needs.

Soleno Inc. produces high-density polyethylene resin pipes used for storm drains and fittings that are shipped throughout Atlantic Canada.

In 2013 the New Brunswick government invested $125,000 in payroll rebates to help replace its assembly line to keep production going[14] McAdam Health Centre, which is adjoined to Wauklehegan Manor, employs approximately 54 employees.

In 2016, Jonny Harris made his celebrity debut at his show at Mcadam High School on CBC’s Still Standing.