The bridge, which crosses the east branch of the Conococheague Creek, is only opened to vehicle traffic four times a year. It's open to pedestrian and bicycle traffic year-round.
"If we left it open all the time, heavy trucks and traffic would cross, which would weaken the bridge," said association member Al Bonnell, who greeted drivers at the bridge's east entrance on Weaver Road in Antrim Township.
"It was built for horses and buggies, not for the big traffic," added Jim Halmi.
By 2 p.m., more than 50 cars, vans and small trucks had passed through the cool, dark interior of the bridge, making a clacking sound as they slowly passed over the floorboards.
A passenger in a minivan, Christophel, like several other local residents, said she drove across the bridge for the sake of nostalgia.
"I have a lot of memories of this bridge," Christophel said.
Parents packed their vehicles with their children, most of whom had never seen or crossed a covered bridge.
Others, who found out the bridge was open while on their way to a nearby park, decided to drive across just for the experience.
"I guess it's unusual ... . There's hardly any covered bridges around really," said association member Mike Mess, who with Elmer Packheiser was handing out pamphlets, selling postcards and other goods, and taking donations from people who crossed the bridge.
In 1991, the local association started a three-year, $80,000 renovation of the bridge, which had been severely damaged and neglected over the years.
"A good strong wind probably would've blown it into the creek," Halmi said.
Workers repaired the cracked and broken center pier, put in steel support beams, replaced the siding and roof and painted the bridge, among other repairs.
The donations collected Sunday will be used for maintenance.
"It's now our responsibility to keep it in one piece so it can be preserved for our grandchildren," Bonnell said.
Martin's Mill bridge was built in 1849 with lumber believed to be cut at a grist and sawmill near the western entrance of the bridge.
The bridge was severely damaged during Hurricane Agnes in 1972, when wind and water swept it from its piers, laying it against the west bank of the creek. It was restored using an estimated two-thirds of its original materials.
The bridge also is opened for vehicle traffic on Memorial Day, Labor Day and around the Christmas holiday.