Green’s Dictionary of Slang

(US) a resident of Omaha, Nebraska.

1876		Silver City (ID) Avalanche 8 Feb. 2/2 : A party of eight [...] Omahogs, or, in other words, citizens of Omaha, left Cheyenne Wednesday for the Black Hills [DA].
1889		Sporting Life (Phila.) 3 July 1/5: [heading] The ‘Omahogs’ Closing In On the Leader—Great Work All Round [DA].
1933		AS (Dec.) 80/2: Out-state newspapers often call the inhabitants of Omaha, Nebraska, Omahogs.
1949		Mencken in AS XXIV 25: Omahog for a citizen of Omaha was invented by the late Sandy Griswold.