The sprawling 150-acre Newman-Swig camp is on Porter Creek Road in the mountains between Santa Rosa and Calistoga.
The camp was scheduled to open Wednesday, but administrators notified parents not to bring their children. About 1,400 campers seven to 17 years of age were expected to attend this summer.
County health officials say flu symptoms appeared in 15 of 160 staff members over the last week.
Two cases are probable and the other 13 are suspect.
"Fortunately, the symptoms in the individuals who have the /*H1N1*/ flu at the camp have been mild. There has been no hospitalization of the individuals who became ill," Sonoma County Director of Public Health Mary Maddux-Gonzales said.
Maddox-Gonzales says the camp took immediate steps to prevent the spread of the flu.
The county is investigating to see how the counselors were exposed to the virus.
The Union for Reform Judaism, which runs the camp, did not respond to inquiries.