San Mateo County is one of a small number of innovative local jurisdictions that is expanding coverage for uninsured adults and at the same time undertaking a reform of its safety net primary care system. We evaluated the impact of the systems redesign by comparing outcomes for a group of people served at the largest county safety net clinic prior to systems redesign (2006) to those served at the clinic after systems redesign (2009). Use of any preventive care services in a year climbed from 25.9 percent to 33.3 percent. Continuity of care also rose significantly, and emergency room use declined. The county's experience provides an example for other communities to follow as they improve the efficiency of health care services for the most vulnerable members of society.