County Executive Robert P. Astorino joined Noel D'Allacco, founder of the program, to help kick off the event.
About 100 girls participated in the first of several dress giveaway events this week.
In its ninth year, Operation Prom has helped thousands of area teens by collecting and distributing gently used (and sometimes unused) dresses, as well as arranging for free tuxedo rentals for boys.
"Operation Prom is a great program," Astorino said. "Westchester County is pleased to continue to cosponsor this program through our Department of Social Services."
The county helps publicize events, provides storage space at a county warehouse in Elmsford for the gowns and allows the free use of the County Center for the dress giveaway.
Operation Prom helps teens from low-income households and those who live in shelters or group homes attend their prom at little or no cost.
The Department of Social Services plays a vital role by connecting young women and men in their care with Operation Prom so that girls can pick out a dress at one of the giveaways.
2013 Dress Giveaway Events: