The 1994 national census reported a total population for this woreda of 30,800, of whom 15,644 were men and 15,156 women; 4,099 or 13.31% of its population were urban dwellers at the time. (This total also includes an estimate for the inhabitants of several rural kebeles, which were not counted; they were estimated to have 9,228 inhabitants, of whom 4,714 were men and 4,514 women.) The largest ethnic group reported in Arero was the Oromo (97.23%); Oromiffa was spoken as a first language by 98.6% of the inhabitants. The plurality of the inhabitants practiced traditional beliefs, with 39.68% of the population reporting answers in that category, while 22.41% of the population said they were Muslim, 4.04% professed Ethiopian Orthodox Christianity, 2.35% were Protestant, and 2.3% were Catholic.