Stacy Alan, 49, and John Poole, 43, said the venue for the wedding was left up to the groom, and he picked the institute's Gallery 240, in front of Georges Seurat's painting "A Sunday on La Grande Jatte," for the Saturday nuptials, the Chicago Tribune reported Tuesday.
"It's kind of my church," Poole said of the museum.
The couple and their about 20 guests said security guards either didn't notice or purposefully looked the other way during the hurried "guerrilla wedding."
"There was no 'dearly beloved.' We just started in on the vows," Alan said.
Museum spokeswoman Erin Hogan said the facility is available for weddings and dinner parties. She said officials are aware of unauthorized weddings like the one that took place Saturday, but they do not mind so long as other patrons aren't disturbed.
"It's kind of cute," she said.