Somalia's first national census was taken in February 1975, and as of mid-1992 no further census had been conducted. In the absence of independent verification, the reliability of the 1975 count has been questioned because those conducting it may have overstated the size of their own clans and lineage groups to augment their allocations of political and economic resources.In the latter case, the sampling units were chiefly watering points. Preliminary results of that census were made public as part of the 3 Year Plan, 1979-81, issued by the Ministry of National Planning in existence at the time. Somali officials suggested that the 1975 census undercounted the nomadic population substantially, in part because the count took place during one of the worst droughts in Somalia's recorded history, a time when many people were moving in search of food and water. The total population according to the 1975 census was 3.3 million. The United Nations (UN) around Somalia's population in mid-1991 at nearly 7.7 million. Not included were numerous refugees who had fled from the Ogaden in Ethiopia to Somalia beginning in the mid-1970s.

The Somali people are separated into numerous clans, which are groups that trace their common ancestry back to a single father. These clans, which in turn are subseparated into numerous subclans, combine at a higher level to form clan families. The clan families inhabiting the interfluvial area of southern Somalia are the Rahanwayn and the Digil, which together are known as the Sab. Mainly farmers and agropastoralists, the Sab include both original inhabitants and numerous Somali groups that have immigrated into this climatically favourable area. Other clan families are the Daarood of northeastern Somalia, the Ogaden, and the border region between Somalia and Kenya; the Hawiye, chiefly inhabiting the area on both sides of the middle Shabeelle and south-central Somalia; and the Isaaq, who live in the central and western parts of northern Somalia. In addition, there are the Dir, living in the northwestern corner of the nation but also dispersed throughout southern Somalia, and the Tunni, occupying the stretch of coast between Marka and Kismaayo. Toward the Kenyan border the narrow coastal strip and offshore islands are colonised by the Bagiunis, a Swahili fishing people.