The donation is the largest to ever be left in the Kansas City area, reported KSHB-TV.
When Salvation Army volunteers counted the money from a kettle in front of a Hy-Vee grocery store, they found the check -- and reason to celebrate.
"Basically, it was a giant Christmas party," said Lt. Kroy Strand, of the Salvation Army Olathe.
A Girl Scout troop had been helping bring in donations that night.
"Singing Christmas carols helped attract more people to donate," said Girl Scout Alexa Bowers.
The donation is expected to go a long way.
"It just means that we'll be able to supply Christmas gifts, food, shelter, utility help," Strand said in a KSHB-TV video.
The Kansas City check is the latest of a few known top dollar Salvation Army donations around the country. Earlier this month, another anonymous donor dropped a gold coin worth $1,300 into a Detroit-area kettle.