It was the first major federal building constructed in the "Inland Empire" that encompasses portions of Washington, Oregon, Idaho, and Montana.

[2] As Spokane continued to grow and postal activity expanded, city officials realized the need to enlarge the building.

[2] The Federal Building and U.S. Post Office in Spokane, Washington, skillfully blends elements of two styles of architecture.

Beaux Arts Classicism and Second Renaissance Revival were popular styles in the early years of the twentieth century.

The building's architect, James Knox Taylor, was a strong proponent of architecture inspired by Classical forms and ornamentation, which he believed appropriately conveyed the dignity of the federal government.

The second and third stories are covered with smooth limestone and feature prominent Tuscan pilasters (attached columns) between window bays.

However, Simon designed the addition using Beaux Arts Classicism and Second Renaissance Revival styles to complement the existing building.

The first floor of the building contains formal public spaces such as the lobby, elevator vestibule, and main staircase.

Marble floors and walls are located in the lobby, and the courtroom features rich details such as Ionic pilasters and decorative plasterwork.

Wide corridors with terrazzo floors and marble baseboards separate perimeter offices from interior light courts.