The Dennis (McCarthy) Hotel is an important example of a traditional style of twentieth century architecture. The 1920s was an era when American architecture reacted to the development of modern styles in Europe and was transforming itself from a richly ornamented historicism to a streamlined modern style. Trained at the Ecole des Beaux Arts (as were Addison Mizner and Henry Dupont) Cunningham's early work reflects the nineteenth-century tradition of historicism. However, he was involved in the design of one of the most important Moderne style buildings of the decade -- the Nebraska State Capitol.

The Dennis Hotel is a 27,000 square foot, eight-story steel frame masonry clad building with seventy-six guest rooms and baths. It is rectangular in plan, with forty feet of street frontage and one-hundred feet of depth. The main (north) facade is sheathed in cast stone and red brick with decorative cast stone and terra cotta ornamentation. The other facades are faced with cement stucco. The base of the Dennis Hotel features a three-story pedestrian level which is the most decorative portion of the building. This portion of the main facade is clad in cast stone and includes six two-story Corinthian pilasters. Behind the corinthian pilasters there was a two story glass wall with wood framing. This wall featured wooden french door with divided light transoms above. Above the Corinthian pilasters is a projecting corinthian cornice line. This entablature had a balcony of wrought iron that no longer exists. The cast stone cladding ends at the third floor with a floor line and a smaller, less ornamented cornice.

The man who built the Dennis Hotel, Nick Dennis, moved to St. Petersburg in 1914. Dennis had been in the hotel and restaurant business in New York and decided to move to St. Petersburg because of its potential as a tourist winter resort. In the general area of Williams Park and First Avenue, Dennis operated the Park Cafeteria and an earlier version of the Dennis Hotel prior to World War I. In 1919, Dennis expanded the Park Cafeteria to a new building at 324 First Avenue North. By 1924, Dennis decided to build a hotel on his cottage site and hired architect Harry Cunningham, whom he had known in Washington, D.C. Work began on the hotel in April 1925; it was completed and opened to the public on December 15, 1925. By this time, most of the rooms had been rented for the season.