Kohn Pedersen Fox Associates designed the casino’s exterior and luxury hotel tower. Rockwell Group produced Mohegan-inspired designs for the gaming area, retail and restaurant boardwalk and hotel lobby. Hirsch Bedner Associates designed the 1,200-room, 34-story luxury hotel interiors and meeting areas.

The multi-use arena at the Mohegan Sun was inaugurated in 2001 under the construction of Perini Building Company. Casino of the Sky opened in September 2001 as an addition to the Casino of the Earth.

Since 2003 ESPN has transmitted live WNBA shows from within the facility.

On January 25, 2005, Mohegan Sun purchased its first gaming business enterprise outside of the state of Connecticut with its $280 million acquisition of the Pocono Downs Racetrack in Plains Township, Pennsylvania.

Mohegan Sun changed the name of the venue to "Mohegan Sun at Pocono Downs" and began a major development. Business as the first slots casino in Pennsylvania, began in November, 2006.

That same month, the tribe revealed plans for a $740 million extension entitled 'Project Horizon'. The project is to be completed in 2010, with parts of the expansion being completed before that. The expansion will add the Casino of the Wind which will include 964 slot machines, 10 table games, and 45 House of Blues poker tables. It will also add 1,000 new hotel rooms, including 300 House of Blues themed rooms complete with its own unconnected lobby.