Iteso traditions relate that they originated somewhere in what is now Sudan and moved south over a period of centuries. It is not possible to calculate the time of this movement. A body of Iteso is said to have separated from the Karamojong and moved further south. This may have been a very early separation because the clan names and ritual customs associated with the second of two distinctive groups of Karamojong and Jie people are not found among the Iteso. Unlike the other Teso-speaking ethnic groups, the Iteso have never been transhumant or nomadic; agriculture has played as significant a role in their social, economic, and expressive lives as cattle have among the other groups.
Iteso clan names reveal a history of long-standing ethnic interactions. Names of Bantu and Northern Nilotic origin are found among them. The Iteso were probably well established in their northern Uganda heartland by the mid-eighteenth century, when they began to move farther south. The history of the Iteso and neighboring peoples has not been extensively documented. Traditions recorded among the JoPadhola indicate there were two waves of Iteso migration. The first was family based and peaceful. It was followed by a more extensive and aggressive migration that left the Iteso in control of a large swath of territory that by 1850 extended as far as the western highlands of Kenya. European travelers record extensive fear of Iteso warriors; nonetheless, the Iteso soon suffered reverses that caused them to draw back to their current territory in Kenya. Since then, the Northern and Southern Iteso territories have been separated. Relations with other societies throughout the precolonial period were alternately peaceful and acrimonious. As a result of spatial intermixture and intermarriage, Iteso elements and customs can be found among neighboring peoples and vice versa. Intermarriage has always been extensive. It is likely that ethnic identity hardened during the colonial period, as it has since, when resources such as land were newly defined as belonging to "tribes."
The Iteso in Kenya and Uganda were conquered by African colonial agents of the British and indirectly ruled through them. Western Kenya was transferred from Uganda to Kenya in 1902. As a result, the economic and political histories of the Northern Iteso and the part of the Southern Iteso living in Kenya have taken vastly different courses. At independence, the Ugandan Iteso were far more wealthy than their Kenyan counterparts. This difference resulted from the status of Uganda as a protectorate reserved for "African development" and Western Kenya's status as a labor reserve for the European-owned farms in the "White Highlands." As a minority people in Kenya, the Iteso are not well known and have been viewed with some suspicion by surrounding peoples. On the other hand, the Kenyan Iteso have not suffered from the political destabilization in Uganda since 1970. Events in the colonial period and since have elaborated cultural differences among the Iteso that were regional in origin. The language of the Northern Iteso, for example, was extensively influenced by the Baganda people, who ruled the Iteso on behalf of the British colonial regime, whereas that of the Southern Iteso is in some ways closer to Turkana. As a result of living among Bantu- and Nilotic-speaking peoples, the Southern Iteso have probably been subject to a greater variety of cultural influences. The economic infrastructure is far more developed in Kenya than in Uganda, and cash income is also higher, reversing a pattern found in the 1960s. The Kenyan Iteso undertook considerable labor migration: most men between the ages of 60 and 80 have worked outside their home territory; many served in places such as Burma during World War II. In the early 1980s government-sponsored cooperatives that ran cotton ginneries in western Kenya failed to pay for cotton delivered by the Iteso and others. Consequently, they began experimenting with new cash crops, such as tobacco, grown with the aid of loans from large agricultural companies. In the early 1990s there was a partial revival of cotton growing, and the ginneries have been resuscitated.