Alldridge first came to Sierra Leone in 1871 and was until the following year acting United States Consular Agent. For several years he acted as Randall and Fisher's agent on York Island, an early trading post of the Royal African Company situated in the channel between Sherbro Island and the mainland. He entered government service in 1889, from November of which year he acted as one of the two travelling commissioners appointed to make treaties with the Chiefs of the Protectorate, a move designed to extend British influence and forestall the spread of French power in the colony's hinterland. His first extended trip was made in 1890, setting off from Sulima and travelling north-east through the Mendi country to Pendeme. During his second trip the following year, he succeeded in settling a dispute between Kai London and Momo Babawo of Pendembu. In 1894 he was appointed District Commissioner for Sherbro and saw much of the fighting during the Hut Tax War of 1898. He retired in 1905. In addition to his official duties Alldridge was a lively observer of the peoples and customs of Sierra Leone and consistently interested himself in the commercial potential of the hinterland, being particularly impressed by the quality of the country cloth manufactured. His published works contain detailed ethnological and economic descriptions of the country. His two major works were The Sherbro and its hinterland (1901) and A transformed colony: Sierra Leone as it was and as it is (1910). As honorary corresponding secretary for Sierra Leone to the Royal Colonial Institute he also contributed articles to the Royal Colonial Institute Proceedings and United Empire as well as writing the Sierra Leone section for the Oxford Survey of the British Empire. Some of Alldridge's activities are narrated in: Fyfe, C. (1962), A history of Sierra Leone, London: Oxford University Press. A detailed account of his treaty making expeditions can be found in: Abraham, A. (1978), Mende Government and politics under Colonial rule: a historical study of political change in Sierra Leone, 1890-1937, Freetown: Sierra Leone University Press.