While some of the volunteers at the shop that raises money for Advocate Good Samaritan Hospital thought the painting was unsellable, volunteer Nancy Shack did some Internet research.
Shack thought she had a Parrish, an American artist born in 1870 and dubbed "the common man's Rembrandt" by Smithsonian magazine, the Chicago Sun-Times reported Sunday.
She contacted Parrish expert, Alma Gilbert-Smith, director of the Cornish Colony Gallery & Museum in New Hampshire and Gilbert-Smith asked her to send the painting for confirmation.
The 1918 painting, done for an advertisement for Swift's Premium Ham that has the fictional Jack Sprat and his wife dining on ham, was confirmed by Gilbert-Smith as an original Parrish.
The proceeds of the painting's sale will go toward the Downers Grove hospital's cardiac catheterization lab.