The oldest concrete-block public building in the United States, the Kamehameha V Post Office pioneered the use of this new material in Honolulu. Knowledge of this construction technology, which was still in experimental stages in France and England, came to Hawaii with J. G. Osborne, a British masonry contractor. The concrete blocks were manufactured on-site. In 1900, a brick addition was placed on the rear of the building, with its exterior walls finished to correspond with the original structure. This Renaissance Revival post office was a social hub for the city, especially when ships bearing mail appeared in port. The blind arcade fronting the first-story lanai once housed a thousand brass lockboxes. The post office served the town until 1922.
Osborne lived in Honolulu between 1866 and 1872. During his stay, this skilled mason designed and/or built a number of commercial buildings as well as the government's coral stone Bonded Warehouse (1867; demolished) and the Hawaiian Hotel (1872; demolished).