 With an estimated area of 545.32 square kilometers, Deder has an estimated population density of 463.1 people per square kilometer, which is greater than the Zone average of 102.6.The 1994 national census reported a total population for this woreda of 179,541, of whom 91,766 were men and 87,775 women; 14,087 or 7.85% of its population were urban dwellers at the time.The two largest ethnic groups reported in Deder were the Oromo (92.12%), and the Amhara (7.43%); all other ethnic groups made up 0.45% of the population.