The casino, along with the nearby National Mississippi River Museum & Aquarium and other attractions, have helped to create a large and growing tourism market in Dubuque.

The name honors businessman Joseph "Diamond Jo" Reynolds, who owned a Dubuque shipping company, among other enterprises.

[6] In September 2006, Peninsula Gaming officials announced that the Diamond Jo would begin a major expansion, during which it would become a land-based casino.

The $75 million project, set to open in November 2008, will include 1,000 slot machines, 17 table games, and a poker room in a new 35,000-square-foot (3,300 m2) casino.

The museum will take over the Diamond Jo's existing Portside Building, as well as the riverboat, and renovate them into an IMAX-like theater and exhibit space.

The Mississippi Moon Bar was named after the refrain in the Doobie Brothers song "Black Water", which the casino uses in their current commercial campaign.