The office floors wrap around a giant cylindrical atrium which extends through the roof to a sloping skylight. The atrium is separated from the plaza by a curved glass wall.
The building houses state government offices, a post office, a rapid transit station serving five train lines, shops, sculptures, a free public art gallery, and a blood donation center.
The columns and granite screens which encircle the base continue around the perimeter of the plaza, decreasing in height the farther they get from the building.
Blue glass, salmon-pink panels, red structural elements, and pink granite give the interior and exterior an eye-catching color scheme.
At the time of its construction the design was a sharp break from convention, with a broad sloping curve of glass sweeping from one corner of the block to the other. The shape has often been compared to a spaceship.
The building's bold design by Helmut Jahn was commissioned by four-term Illinois governor James R. Thompson, after whom the building is named.
Just inside the main entrance a waterfall pours down to the lower level between a pair of escalators.
Glass elevators with vaulted tops shuttle passengers up and down a pair of elevator bays that project into the atrium.
The basement level holds an auditorium and a large food court which opens onto the atrium.
A two-story open gallery encircles the entire building at sidewalk level, with round columns screened by flat granite panels.
Conceived as a futuristic reinterpretation of the state capitol form, the building's skylight and central atrium stand in for the traditional dome and rotunda.
The plaza features the Jean Dubuffet sculpture Monument With Standing Beast, a 4-piece amorphic fiberglass construction painted white and crossed by a web of black lines.