Gala co-chairs Laura Ferris Anderson, managing partner, JPMorgan Chase & Co.; and Bryant Keil, founder and chairman, Potbelly.

Logan LaHive, CEO of Belly, the hot rewards-card startup, is a compliant fellow. He attended Wednesday evening’s Chicagoland Entrepreneurial Center’s Momentum Awards dinner without a tie, as the invitation suggested. In fact, Mr. LaHive didn’t even bother with a dress shirt.

The dinner was billed as a networking event; Mr. LaHive viewed it as more of a party. “I’m not here doing business – I’m catching up with people who have helped me along the way,” said Mr. LaHive, who wore an orange T-shirt under his sport coat. “This is an opportunity for me to catch up with great folks.”

Mr. LaHive was one of 750 entrepreneurs, bankers, venture capitalists and assorted friends who attended the gala at Millennium Park. Festivities began on the Harris Theater rooftop with a cocktail party. The feeling was entrepreneurial-modern, complete with clusters of white furniture (ignored) and a ping pong table supplied by Killerspin.

Leslie Anderson, managing director at BMO Harris Bank, one of the gala’s major sponsors, viewed the event as part fun, part networking. “A lot of these are startups,” Ms. Anderson said of the assembled. “Everybody needs a bank.”

Dinner (iceberg wedge salad, horseradish-crusted filet) was served in a tent on the park’s North Promenade. It began briskly enough, with remarks by Kevin Willer, CEC president and CEO, and an energetic talk from a tieless Mayor Rahm Emanuel.

“Four years ago you couldn’t have had a dinner like this,” the mayor said, adding that Chicago now has the ecosystem of entrepreneurs, venture capitalists, universities and the digital capabilities necessary to nurture new business. “Not a city in the country will beat the city of Chicago,” he declared, leaving the stage to the strains of “A Hard Day’s Night.”

The evening slowed considerably during the presentation of the Entrepreneurial Champion Award to Michael Ferro, chairman of Merrick Ventures and founder of the evening’s Merrick Award. A speech, a video clip featuring Jim Belushi and Dan Ackroyd dressed as the Blues Brothers, and Mr. Ferro’s wry acceptance speech – “It seems funny to get an award I invented” – consumed almost a half-hour of the evening.

The big-thrill moment for the entrepreneurs in the room was the Merrick Momentum Award. Local startups Trunk Club, a by-mail apparel-shopping service for men; Braintree Inc., a provider of online and mobile payment systems; and Narrative Science Inc., which converts data into stories, were finalists.

The winner: Braintree. “This is part of a larger story,” said Bryan Johnson, founder and chairman, as he accepted the award. He was referring to the hundreds of entrepreneurs in the audience as well as an even brighter future for his company. The Momentum Award can work wonders for winners; IfByPhone, one of last year’s runners-up, raised an additional $2 million in financing after the dinner.

After dinner, some of the 750 gala guests returned to the Harris rooftop to join Next Wave, a $100-per-ticket after-party for budding entrepreneurs. CEC sold 150 tickets, twice the number expected.

The gala grossed $1.5 million – including $26,000 from a text-donation solicitation at the dinner – to fund Chicago Entrepreneurial Center programs. Crain’s Chicago Business was one of the evening’s 43 silver sponsors.