Sonoma County is committing to constructing a new five-story government headquarters building for $308-million. It will be built on the county’s existing government campus on Administration Drive. The county is also planning to build a mixed-use residential and commercial development on the property. The headquarters building is planned to be smaller than the county initially envisioned. So, Sonoma County will also be buying existing office space in the area to house offices that won’t be able to fit in the new building.