The original December 12, 2022 item:
The Katzenjammer Kids first appeared December 12, 1897.
The comic strip was created by Rudolph Dirks and New York Journal editor Rudolph Block. Various cartoonists (Harold Knerr, Oscar Hitt, Doc Winner, Joe Musial, Mike Senich, Angelo DeCesare, Hy Eisman) continued it’s Sunday run until sometime in 2006 when new episodes were replaced by reruns. The reruns by Hy Eisman continue to run online at Comics Kingdom but there is no evidence that any newspaper, at least in the U.S., still runs the comic. The reruns were replaced by Prince Valiant on the King Features Weekly Service schedule in 2015.
With 108/109 years of new strips (1897 – 2006) The Katzenjammer still holds the title of the longest running comic strip. Though Gasoline Alley at 104 years (1918 – present) is creeping up on The Kids.
December 21 Update
Kristian Hellesund, in his essay celebrating the quasquicentennial of The Katzenjammer Kids debut has discovered what he thinks is the final new KatzKids Sunday page by Hy Eisman.
Google translate: “There is some uncertainty as to what is the very last Sunday page with Katzenjammer Kids. In all likelihood it is this one, which is dated 16 July 2006.”
How he came to that conclusion? I don’t know.