Eighty-six men, women and children were killed, and more than 120 were injured. The dead included a lion tamer, strongmen, a trapeze artist and clowns, along with workers who set up and broke down the traveling Hagenbeck-Wallace Circus, one of the biggest in the U.S. at the time.

Though it remains one of the most deadly railroad disasters in U.S. history, the train wreck is also remembered for what happened next. It spurred other circuses to send performers that helped Hagenbeck-Wallace put on shows scheduled as soon as two days after the crash. The tragedy also rallied a fraternal order of entertainers, the Showmen’s League of America, that continues to preserve traditions of outdoor show business and honor its dead.

“We’re all traveling people. That’s the thread,” says Jimmy Drew, who furnishes rides to fairs in 10 states. Of the kinship with the 1918 circus casualties, he says, “we have to remember who we were to know where we’re going.”

Showmen’s League members, many of them operators of family-owned carnivals that travel the country, gathered last month at Woodlawn Cemetery in this Chicago suburb to mark the centennial of the wreck. In a coincidence that forever linked the 105-year-old group to the disaster, the Showmen’s League bought a cemetery plot shortly before the wreck.

It named the plot Showmen’s Rest, intending it as a final home for entertainers, many of whom were rootless. That June, however, the League offered it as a mass grave for those who died in the Hagenbeck-Wallace wreck, which occurred about 25 miles away from Chicago.

In the cemetery, bordered by five sculptures of elephants with their trunks lowered in mourning, rows of plaques commemorate the victims, some with just nicknames or circus duties. “Baldy” lies next to “4 Horse Driver.” Dozens are anonymous, bearing only a number and “Unknown Male” or “Unknown Female.”

The May ceremony was held a month before the anniversary so more League members could convene before the summer carnival season kicked off. At a podium beside a live circus band and a century-old gilded horse cart, Father John Vakulskas Jr. led a prayer as League members laid out a flowered wagon wheel with a missing spoke, a symbol of loss.

Mr. Vakulskas is a Catholic priest who travels the country ministering to the carnival community—blessing rides and games, leading masses in Spanish and English, baptizing the children of itinerant workers. He wore a stole embroidered with a carousel horse, a ferris wheel and other emblems of traveling shows.

Afterward, he spoke of lingering misperceptions about carnival workers and why they take offense at “carny.” “It’s a pejorative,” he said.

The Showmen’s League straddles two worlds. Consider its headquarters. Eight years ago it bought a building in Chicago’s former meatpacking district, Fulton Market, which soon took off as one of the city’s trendiest neighborhoods. The group’s airy office, where a large painting of its first president, Buffalo Bill Cody, greets visitors, is across the street from a Google office and near some of Chicago’s hottest restaurants and bars.

When members assemble, they are just as likely to talk about new rides, games and food trailers as current business concerns, especially the federal cap on the number of non-agricultural guest workers granted visas. Carnivals and circuses rely heavily on these seasonal employees, many of them from South Africa and Mexico, to run each summer.

“It’s extremely hard to get good labor that will travel, pass a drug test, a criminal background check and only work six months,” says Bill Johnson, a former Showmen’s League president and the owner of Fantasy Amusement Company, a 33-year-old amusement park that operates around Illinois and Indiana.

There are an estimated 250 organized carnivals in the U.S., part of a broader mobile amusement industry generating an annual $3.15 billion in revenue, according to industry trade group the Outdoor Amusement Business Association. Nearly half of its roughly 15,000 seasonal workers are foreign, with many returning to the same employers annually. But one-third of the industry’s visa requests went unfilled last year.

Some things that carnivals compete with are relatively new—casinos, Netflix , smartphone apps—but the core challenges haven’t changed drastically over the past century.

“We’re not that much different than farmers and ranchers. We’re seasonal, we depend on the weather, and all our money comes in a short amount of time,” says Guy Leavitt, current president of the Showmen’s League.

Mr. Leavitt’s children represent the third generation of his family to work for Ray Cammack Shows, a carnival operator started in 1961 by his father-in-law. It travels from fair to fair with two teachers that run a mini school—preschool through 8th grade—for children of its 400 employees.

The arcana of their industry unites “show people” almost as much as the family ties. Mr. Drew, who operates Drew Exposition, a traveling amusement park based in Augusta, Ga., was so enamored of a ferris wheel made for the 1962 World’s Fair that he put an illustration of it on his company’s letterhead four years before he bought one.

“My mouth would drop open to look at that machine,” said Mr. Drew, 72 years old, whose company began with one carousel purchased by his mother and father in 1948.

The Showmen’s League has about 1,100 members, down from a peak of about 1,500. These days it puts more of a priority on granting college scholarships and other services, but it still offers a burial ground. There are many plots remaining at Showmen’s Rest.

At the cemetery, Mr. Johnson, the former League president, pointed out the plot he bought for himself. It is a few steps away from the graves of the Hagenbeck-Wallace wreck victims and right next to that of his late mentor, Bill Knight.

Mr. Knight brought Mr. Johnson into the business, hiring him at age 12 to pick up balls on the milk-bottle game and later manage a dart game for a cut of the profits.

“I’ll be honored to be close to him,” Mr. Johnson said. “Hopefully we’ll see each other again someday and cut a few jackpots,” carnival lingo for swapping stories.

Write to John Jurgensen at john.jurgensen@wsj.com