Derby Castle Depôt is the main location of workshops and running sheds of the Manx Electric Railway on the Isle of Man and lies at the northerly end of the promenade at Douglas; it takes its name from the adjoining site which was once home to the Earls of Derby, rulers of the island, and later extended to form an entertainment complex of the same name before being demolished and replaced by the ill-fated Summerland complex in 1968.

The location of the depôt can be seen from across the sweep of Douglas Bay and is marked by a large illuminated sign with the words "Electric Railway" in the cliffs above the sheds.

For Scenery", and a similar sign denoting the presence of Derby Castle was located on the hillside approximately behind the Strathallan Hotel (now the Terminus Tavern near the station).

As part of the management's continued commitment to refurbish and improve facilities on the railway, the upper car sheds which had been built between 1894 and 1924 were completely demolished and new versions constructed on the same site.

The overhead wiring also caused difficulties but ultimately the new fully functioning carshed is a vast improvement on the original which had decayed beyond economic repair.