In 1868 Zanetta acquired another piece of property facing the plaza. The old adobe building on the property may have housed cavalrymen, and even earlier served as a monjerio or dormitory for unmarried mission Indian women. Zanetta used the adobe bricks to form the ground floor of a two-story building that he hoped would become the county courthouse of newly established San Benito County.

After Hollister was chosen as the county seat, the first floor of Plaza Hall was modified to serve as the residence of the Zanetta family, while the second floor was used for public meetings and celebrations. Laid over 30-foot-long redwood beams, the floor of the upstairs hall had good "spring" and therefore became famous as a dance floor. Many a grand ball was held there as were political rallies, temperance meetings, traveling shows, and gatherings of local groups such as the volunteer firemen.