Among them is TV personality, actor and designer Carson Kressley.
The Allentown native is competing in the show and has a long family history of equestrian events.
Carson has been competing here for more than 40 years with Saddlebred horses.
This year, he's competing with Beau, a horse his family raised on their farm in the Lehigh Valley.
"He's been a national champion," Kressley explains. "We've raised world champions. We have been doing this a long time and not everybody knows this side of me. It's the most fun, and Devon is the 'granddaddy' of all American horse shows. It started in 1896 and our family has been competing here since the 70s -- so 50 years."
He showed us a family photo from the early 1900s. Four generations of his family have competed at Devon.
"I have shown in so many different divisions here at Devon," he says. "This is something called show "pleasure driving." It's supposed to be fun, but it's nerve-wracking."
Moments before showtime, Kressley ran into another well-known competitor, Teddi Mellencamp from Real Housewives of Beverly Hills.
She's here for Thursday's derby.
"I showed here growing up as a junior rider," Mellencamp explains. "This is the first time I've been here in 25 years."
Carson and Beau took home third place in Wednesday's competition.
The Devon Horse Show and Country Fair runs through Sunday, June 2.