What is the name of Frank Lloyd Wright's first Prairie-style house?

Frank Lloyd Wright's first Prairie-style house was the Ward Winfield Willits House.

Designed in 1901 for businessman Ward Winfield Willits, the house stands in Highland Park, Illinois, north of Chicago. It is commonly called the Ward W. Willits House or simply the Willits House. Historians describe it as one of Wright's first fully realized Prairie School designs, emerging after several years of experimentation.

Its cruciform, or windmill, plan organizes rooms around a central fireplace and extends outward toward porches and terraces. Low rooflines, strong horizontal emphasis, art glass, wood screens, and integrated furniture express ideas that became hallmarks of Wright's Prairie work. Wright designed much of the interior, including furnishings and lighting.

The house is sometimes confused with the Robie House or Dana-Thomas House, both celebrated Prairie-style buildings. Those came later: the Robie House was designed in 1908–09, while the Dana-Thomas House was built in 1902–04. The Willits House is therefore the best canonical answer for Wright's first true Prairie-style house.