Diamond Jo Boat Store and Office, also known as the Dubuque Tank Terminal Co. and Inland Molasses Co. Operations Office, is a historic building located in Dubuque, Iowa, United States.

This is the last remaining structure in the city that is associated with the steamboat era on the Mississippi River.

Originally headquartered in McGregor, Iowa, Joseph Reynolds started in the steamboat business after the American Civil War shipping wheat Minnesota and the Chicago and Northwestern railhead at Fulton, Illinois.

The offices were located on the east end of the simple, two-story, brick building, and the rest was used for storage.

This article about a property in Dubuque County, Iowa on the National Register of Historic Places is a stub.