The right-handed pitcher was traded to the Rangers on Tuesday, and made his American League debut on Thursday. In a full-page ad in the Chicago Tribune, Dempster, who joined the Cubs in 2004, said farewell. The message was titled "Thank you, Chicagoland!"
"Thank you for welcoming me, my family and the Dempster Family Foundation with open arms," Dempster said in the ad. "Your support over the years means the world to us. We will always have fond memories of our years in Chicago.
"A special thanks to the Ricketts family, the Chicago Cubs organization and my teammates -- past and present -- for their support over the years as a member of one of the greatest sports franchises in the world," he said.
"Although I will be playing baseball in another city, our Foundation remains committed to our mission here, and we look forward to being a part of this community for years to come. Chicago has always been my kind of town."
In 2 1/2 years, the Dempster Family Foundation has awarded more than $390,000 to 18 organizations in need in the Chicago area and throughout the country. Dempster established it after his daughter, Riley, was diagnosed with a rare disorder known as DiGeorge syndrome, or 22q.
There now are official 22q clinics supported by the Dempster Family Foundation in Chicago at the Ann & Robert H. Lurie Children's Hospital and at Advocate Hope Children's Hospital, and five others nationwide, including the Children's Hospital of Philadelphia, Children's Hospital of Atlanta, Nationwide Children's Hospital in Ohio, Colorado Children's Hospital, and at University of California-Davis.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.