"I probably set a record for the least amount of money donated to it," he joked.
CCFA spokeswoman Ariella Levine confirmed that Knowlton had contacted them about running for awareness, and that they helped him raise money through their half-marathon program.
"Every penny counts so we're happy to take whatever he's able to donate," she said. "It definitely was something that was different and out of the ordinary."
Knowlton, who was greeted in Key Largo on Saturday by his parents and girlfriend -- and a police escort as he ran over the final bridge -- has plans to relax until Friday and then board a plane back to Minnesota.