The Post Office building is a one-story elliptical building near the entrance to the complex.
Its facade repeats the arch motif, with circular embellishments on its canopy.
The interior features an elliptical lobby.

The nearby Veterans' Memorial Auditorium was designed by the Taliesin Associated Architects and was completed in 1971 in a manner compatible with the main complex.
The auditorium was designed for use by the county fair with a combination of flat-floor exhibition space and tiered seating spaces, using a compromise plan devised by Wesley Peters, George Izenour, and Aaron Green.
The main hall seats 1960  in an amphitheater arrangement.
A separate Showcase Theater seats 300, and the exhibition hall can accommodate up to 2000 patrons.

The original Hall of Justice design incorporated the Marin County Jail.
As the jail outgrew its space a number of proposals were advanced for a new facility adjoining the Civic Center.
 A new, mostly underground jail was completed in 1994 in the hilltop immediately to the west of the Hall of Justice, designed by AECOM with 222 cells and 363 beds.
The jail connects to the Hall of Justice by an underground link.
The design concept was originally suggested by Aaron Green.
The final design was reached after unsuitable underground and above-ground designs were rejected in the 1980s.
Natural lighting of interior spaces is provided by skylit light wells over the common space of each of six pods.

A Sonoma–Marin Area Rail Transit train station was constructed nearby which bears the same name.
The Post Office building is a one-story elliptical building near the entrance to the complex. Its facade repeats the arch motif, with circular embellishments on its canopy. The interior features an elliptical lobby.
The nearby Veterans' Memorial Auditorium was designed by the Taliesin Associated Architects and was completed in 1971 in a manner compatible with the main complex. The auditorium was designed for use by the county fair with a combination of flat-floor exhibition space and tiered seating spaces, using a compromise plan devised by Wesley Peters, George Izenour, and Aaron Green. The main hall seats 1960  in an amphitheater arrangement. A separate Showcase Theater seats 300, and the exhibition hall can accommodate up to 2000 patrons.
The original Hall of Justice design incorporated the Marin County Jail. As the jail outgrew its space a number of proposals were advanced for a new facility adjoining the Civic Center.  A new, mostly underground jail was completed in 1994 in the hilltop immediately to the west of the Hall of Justice, designed by AECOM with 222 cells and 363 beds. The jail connects to the Hall of Justice by an underground link. The design concept was originally suggested by Aaron Green. The final design was reached after unsuitable underground and above-ground designs were rejected in the 1980s. Natural lighting of interior spaces is provided by skylit light wells over the common space of each of six pods.
A Sonoma–Marin Area Rail Transit train station was constructed nearby which bears the same name.
Marin County Civic Center