Stretching 120 feet from the floor to the skylight, the Statehouse Rotunda is by far one of the grandest spaces in the Statehouse. The rotunda is located below the cupola, which is itself an architectural feature unique to Ohio's Statehouse. The cupola is the two-story, drum-shaped pinnacle with a low conical roof. The rotunda ceiling is 67 feet lower than in the United States Capitol Building in Washington D.C.

A 29-foot-wide skylight crowns the rotunda. The skylight features a hand painted image of The Great Seal of Ohio in the center. First designed in 1847, the state seal has changed several times in the course of Ohio’s history. Mountains, a sheaf of wheat, and a bundle of arrows are depicted in the current state seal. The 1861 seal, which is displayed in the rotunda skylight, also includes a canal boat in the foreground. Canals were an important mode of transportation in Ohio at the time.

The rotunda's intricate tile floor is composed of more than 5,000 pieces of hand-cut marble from around the world and holds rich symbolism. The salmon stones are from Portugal; the black and green marble is from Vermont; and the white marble is from Italy. The thirteen center stones represent the original colonies. The three marble bands represent the three major phases of the United States' growth across the continent prior to the floor design in 1858. These include significant territorial expansions following the American Revolution, the Louisiana Purchase and a series of events after 1846 – the Mexican War, the Oregon Settlement and the Gadsden Purchase.