Abstract: This annotated transcription makes available for the first time the unpublished 1821 diary of Sierra Leone by the American Methodist missionary Daniel Coker (1780–1846), a valuable resource for scholarship on American-West African interchange in the 1820s. The diary records genealogical information about native African and colonial American figures; the customs and international reputations of West African royalty; the political relations between West African populations and American colonists; the territorial, social, and religious aims of the American Colonization Society (ACS); the medicine, disease patterns, and climate of Sierra Leone as experienced by Americans; and the seizure and relocation of enslaved people in Fourah Bay by British and American privateers. Complementing the recent discovery of the ACS’s land treaty for Liberia, Coker provides an intimate glimpse of the major players, colonial aims, and local response surrounding that acquisition. This diary also portrays a rare perspective on America’s federal colonial project: that of a Black American community leader.