A new exhibit at the Scott County Historical Society chronicles the 40-year history of Valleyfair, the 125-acre amusement park nestled southwest of the Twin Cities in Shakopee.

From dolphin shows to 200-foot roller coasters, the key to the park’s success has been its constant evolution, adding new attractions to meet changing visions of entertainment, said Kathleen Klehr, executive director at the Scott County Historical Society.

Called “Valleyfair: 40 Years of Fun,” the exhibit resonates “because virtually everybody knows about Valleyfair,” Klehr said. “It’s the largest amusement park in the Upper Midwest — and it’s grown every year.”

The memorabilia on display include an old car from the High Roller roller coaster, a vintage ring toss and an oversized Colonel Ohoom Pa Pa costume; he was the park’s onetime mascot.

The display, which runs through October, is a collaboration between the Historical Society and Valleyfair, which donated more than 800 items to the county along with funding for research. And the Historical Society already had a few items.

But it’s not all past history. In addition to artifacts from the ’70s and ’80s, there are a few employees who could themselves be part of the exhibit, because they worked at Valleyfair when it opened and are still there.

“It’s been such a fun ride the whole time,” said Tom Suel, who got a job at Valleyfair 40 years ago and is now the maintenance director. “There’s so much variety here and different things going on, it’s hard not to love it.”

In 1976, Valleyfair debuted on the banks of the Minnesota River with 26 acres of rides and attractions. Two businessmen developed the park with a family-oriented, county fair concept in mind. Employees wore knickers and long dresses intended to look like Coney Island-style outfits circa 1900, said Dave Frazier, general manager.

Valleyfair was sold in 1978 to Cedar Fair, a company that already owned Ohio’s Cedar Point amusement park and later created a chain of amusement parks.

Over 40 years, the number of roller coasters has increased to eight and total attractions to 75. Something new has been added nearly every year, Klehr said.

Wild Thing, still the park’s most popular ride, came in 1996, and its popularity spurred several years of attendance growth, Frazier said, though he wouldn’t reveal past or current attendance totals.

The biggest change over four decades has been the technology behind the park’s rides, now all computer-operated, Frazier said.

Along the way, some rides and shows have been removed as they became outdated, including the log flume, the Skipper and Dolly Dolphin Show, a performance featuring “high-diving hillbillies” and a petting zoo.

Suel, who once transported the dolphins, said he misses them.

While the park may change, it can’t expand physically, since it borders the river, the highway and a small airport. It’s one-third the size of some other parks in the Cedar Fair chain, Frazier said.

Another challenge: The park sits in a flood plain, and some areas are under water when there’s heavy rain, Frazier said.

Despite the automation of many rides, the park still employs thousands of people, including 1,600 seasonal workers, nearly double the number when it opened. There are also 80 full-time employees.

Valleyfair is a family, Frazier said, which is why he came back after being employed there as a teen.

It will be around for a long time, he said.

“Valleyfair is just going to grow and change with what this market wants,” Frazier said. “For the Minneapolis area, there’s nothing to compare it to.”

This year, Valleyfair opens for the season on May 13.