Comic Book Cats, number 120: Famous Funnies #1, written & drawn by Clare Victor Dwiggins, published by Eastman Color in July 1934.
A big “thank you” to David Welsh who informed me of this historic cat page from the dawn of comic books. David provided the following explanation:
“Famous Funnies #1  is often cited as the first “modern” comic book following the Platinum Age. By that metric, this reprint of a 1933 Sunday page of Nipper by Clare Victor Dwiggins (as Dwig) is the first cat in comic books.”
Famous Funnies is, as David states above, generally considered by historians to be the first true American comic book. An anthology title, the first issue was 68 pages with a 10 cent cover price that collected together a number of different newspaper strips from the Ledger Syndicate. Beginning with issue #2 it began to also contain original material created specifically for the title. Famous Funnies ran for 218 issues, ending in July 1955.
Born in Wilmington, Ohio on June 16, 1874, Clare Victor Dwiggins worked on a number of different comic strips and single panel gags in a career that stretched from 1897 to 1942. Nipper was a daily & Sunday comic strip distributed by the Ledger Syndicate that ran from 1931 to 1937. Dwiggins passed away on October 26, 1958 at the age of 84.
The entire issue of Famous Funnies #1 can be viewed on The Digital Comic Museum.