More than 2,000 people came out for the annual commemoration of the park's 1977 reopening, said Lori Taylor, parks coordinator for Washington County Department of Recreation and Parks.
"Everybody's Day is a picnic for everybody - entertainment for children as well as older people - a tradition that's been going on for years at the county's most beautiful park," said Rachel Mobley, administrative assistant for Washington County Department of Recreation and Parks
"We try and get that old feeling back for the day, and I think we do it," Taylor said.
Benjamin Kauffman and partner Myrtle Seville left the dance floor and then talked about going back.
"It's a lot of fun. If I was a lot younger - I didn't start out soon enough," said Kauffman, 82, from Fayetteville, Pa. "I've got a knee replacement. Got to get it loosened up now and then, and have a little fun while I can."
Seville, 68, said she started dancing with Kauffman about four years ago. This year is her third year at Pen Mar.
"It's a happy occasion, and friendly," said Seville, of Chambersburg, Pa., while resting between dances. "Everybody does everything different. But you've got to dance to the beat. You can do anything you want to if you dance to the beat."
Far behind the pavilion, another type of dancing was going on.
A huge white tepee was the gathering spot for Native American history enthusiasts watching performances by the Potamac Indian Dancers of Explorer Post No. 2.
Visitors also viewed Hagerstown Roundhouse Museum and the Cumberland Valley Woodcarvers exhibits.
The Beale Street Puppets, a Baltimore-based group, entertained children and the young-at-heart with "Teddy Bear Circus" show.
And look-but-don't-touch signs preserved the Miniature Carousel Builders Inc. display of 16 fanciful carousels.
"We've been coming here for years," said founding member Jerry Defenderfer, 66, of Chambersburg. "It keeps getting bigger."
Fellow carousel builders Charlie and Georgia McDaniel, both 63, of Poquoson, Va., drove about five hours to Pen Mar.
They brought their 32-figure Virginia Carousel, complete with music, lights, moving horses and tiny painted Virginia scenes: Monticello, Virginia Beach, the Navy Yard, Williamsburg and of course, Poquoson.
About half the crowd brought lawn chairs and focused on the music.
Melvin and Naomi Brucksch came straight from Mountain Church in Joppa, Md., and relaxed in lawn chairs near the edge of the overlook.
"We always enjoy the band, and it's such a nice, clean park," said Naomi Brucksch.
The Bruckschs, of Abingdon, Md., said they've enjoyed the park for a half century.
"The best thing they started was when they got people to donate the benches - we used to have to sit on the grass," said Melvin Brucksch. "People come for the memories ... when we were young and the friends we were with."