Oromia (sometimes spelled Oromiya and spelled Oromiyaa in the Oromo language) is one of the nine ethnic divisions (kililoch) of Ethiopia. Covering 353,632 square kilometers stretching from the eastern border in an arc to the southwestern corner of the country, its population was estimated in 2002 at about twenty-four million, making it the largest state in terms of both population and area. It includes the former Arsi Province along with portions of the former Bale, Hararghe, Illubabor, Kaffa, Shewa, Sidamo, and Welega provinces. Its current capital is Adama; other important cities and towns include Ambo, Asella, Debre Zeit, Dembidolo, Fiche, Gimbi, Goba, Jimma, Metu, Negele Boran, Nekemte, Shashamane and Waliso. This region embraces most of territory of the Oromo people, who had migrated in the 16th century from east of the Great Rift Valley into the Omotic-speaking areas of western Oromia, as well as to the northeast at least as far as Harar. Prior to 2000, the Regional capital of Oromia was Addis Ababa, also known as "Finfinne" (the original name in the Oromo language). The relocation of the regional capital to Adama sparked considerable controversy. Critics of the move believed the Ethiopian government wished to deemphasize Addis Ababa's location within Oromia. On June 10, 2005, the Oromo Peoples' Democratic Organization (OPDO), part of the ruling EPRDF coalition, officially announced plans to move the state capital back to Finfinne. This boundary has been disputed with Oromia's neighbors in a number of cases, most notably between Oromia and the Somali Region. One attempt to resolve the dispute between the two Regions was the October, 2004 referendum held in about 420 kebeles in 12 woredas across five zones of the Somali Region. According to the official results of the referendum, about 80% of the disputed areas have fallen under Oromia administration, though there were numerous allegations of voting irregularities in many of them. In Oromya, estimates based on figures given by local woreda and kebele authorities suggest that a total of 21,520 people have been displaced in different border woredas, namely Mieso, Doba, and Erer in the Mirab and Misraq Hararghe Zones. In Doba woreda, the Ministry of Federal Affairs put the number of IDPs at 6,000. There are also more than 2,500 displaced persons in Mieso.


Based on the 2007 Census conducted by the Central Statistical Agency of Ethiopia (CSA), Oromia has a total population of 27,158,471, consisting of 13,676,159 men and 13,482,312 women; urban inhabitants number 3,370,040 or 11.3% of the population. With an estimated area of 353,006.81 square kilometers, this region has an estimated population density of 76.93 people per square kilometer. For the entire region 5,590,530 households were counted, which results in an average for the Region of 4.8 persons to a household, with urban households having on average 3.8 and rural households 5.0 people. Ethnic groups include the Oromo (87.8%), Amhara (7.22%), Gurage (0.93% - some of Sebat Bet Gurage, Soddo Gurage, and Silt'e); the remaining 4% constitute other ethnic groups. 47.5% were Muslim, 30.5% Orthodox Christians, 17.7% Protestants, 3.3% followers of traditional religions and 1.1% all other religious groups; in urban areas, Orthodox Christians constitute 51.2% of the population, followed by Muslims at 29.9%, Protestants 17.5%, and all other religious groups at 1.5%. In the previous census, conducted in 1994, the region's population was reported to be 18,732,525, of whom 9,371,228 were men and 9,361,297 women; urban inhabitants number 621,210 or 14% of the population. 44.3% were Muslims, 41.3% Orthodox Christians, 8.6% Protestants, and 4.2% followers of traditional religions. The remaining 1.6% constitute other religious groups; in urban areas, Orthodox Christians constitute 67.8% of the population, followed by Muslims at 24.0%, and Protestants 7%.
The major ethnic groups within the State were the Oromo (85%), Amhara (9.1%), and Gurage (0.98%); 4.6% constitute all other ethnic groups. However figures of full ethnic background are disputed, since many ethnically mixed Ethiopians are difficult to categorize. Particularly, Shewa Oromos and urban Oromos are known to have assimilated with ethnic Amhara and others, while southwestern Oromos have mixed with the Sidama and other ethnicities. For instance, mixed Ethiopians with Oromo father and Amhara mother are registered into the census using only their father's ethnic label. Oromo (Oromiffa), presently written with Latin characters, is the most commonly spoken language, constituting 83.5% of the spoken language. (especially in eastern Welega and northern Shewa), Gurage languages (Sebat Bet Gurage, Soddo, Silt'e), Hadiya, Gedeo (0.98%), especially in western and eastern Shewa; and Tigrigna (0.25%). OmoticAccording to the CSA, as of 2004[update], 32% of the total population had access to safe drinking water, of whom 23.7% were rural inhabitants and 91.03% were urban.


The CSA reported that for 2004-2005 115,083 tons of coffee were produced in Oromia, based on inspection records from the Ethiopian Coffee and Tea Authority. This represents 50.7% of the total production in Ethiopia. Farmers in the Region had an estimated total of 17,214,540 cattle (representing 44.4% of Ethiopia's total cattle), 6,905,370 sheep (39.6), 4,849,060 goats (37.4%), 959,710 horses (63.25%), 63,460 mules (43.1%), 278,440 asses (11.1%), 139,830 camels (30.6%), 11,637,070 poultry of all species (37.7%), and 2,513,790 beehives (57.73%). According to a March 2003 World Bank publication, the average rural household has 1.14 hectares of land compared to the national average of 1.01 hectares, 24% of the population is in non-farm related jobs compared to the national average of 25%.