The Marin County Civic Center, consisting of the Administration Building and the Hall of Justice Building, is the last major work of Frank Lloyd Wright, and one of the finest expressions of organic architecture, a concept that Wright labeled as his own.

The Marin County Civic Center is the largest constructed public project of Wright's career and the only one for a governmental jurisdiction. A United States Post Office in the complex is the only federal commission ever executed by Wright, who, ironically, was the first architect to be represented on a postage stamp.

The Marin County Civic Center complex is composed of two long wings set at a 120 degree angle to each other and hinged together by a rotunda with a shallow dome backed by a 172-foot, triangular tower. The form of this complex embodies Wright's belief in democratic values that place human services above the regulatory instruments of government. This belief is expressed by the visual dominance of the Administration wing, which, although shorter than the Hall of Justice wing faces the main access road so that most of the cars pass through its single broad arch on the way to the main parking lot and other parts of the grounds.

Beneath the dome, which is the pivotal element of the plan, is the county library; the adjacent tower was originally meant to transmit radio programs. Thus, the two branches of government meet at the place of dissemination of knowledge and information. Since this central node is also backed by a terrace with a pool outside the cafeteria where employees may relax or eat, "the power and authority of the state ... find their raison d'etre in the wisdom of the citizenry from which, architecturally at least, their expressions emanate."

The Marin County Civic Center is also a National Historic Landmark and California Historical Landmark 999.