Postal service was established in Keswick in Keokuk County, Iowa, on November 12, 1879. Mail volume at the local post office increased on July 1, 1902, when rural free delivery was established in Keswick and six other Iowa communities. Keswick’s one carrier route spanned 23 miles, serving 810 area residents. The establishment of the rural route resulted in discontinuation of the post office location in nearby Ambrose in adjacent Iowa County.

The Keswick Post Office moved to its current location in 1965, when a downtown building was restored by two residents and leased to the US Postal Service.