The population of Tajikistan (2001 estimate) is 6,578,681, giving the republic an average population density of 46 persons per sq km (119 per sq mi). The lowlands of northern and western Tajikistan are the most densely populated areas. Large cities include Dushanbe, the capital, a modern city located in the Hisor Valley of western Tajikistan; and Khujand (named Leninabad from 1936 to 1991), an important cotton-processing center located in northern Tajikistan’s Fergana Valley. Tajikistan was the least urbanized republic of the former USSR. In 1999 only 33 percent of the population lived in urban areas. From the late 1950s strong urban growth, fed by immigrants from other republics, was matched by rapid growth in the rural population. Between 1959 and 1989, the population of the republic increased by more than 100 percent due to a high birthrate and improvements in medical care. During the early 1990s, however, the growth rate began to decline due to civil war and emigration.

On the basis of language, customs, and other traits, the Tajiks can be subdivided into a number of distinct groups. The Pamir Tajiks within the Gorno-Badakhshan autonomous region include minority peoples speaking Wakhi, Shughni, Roshani, Khufi, Yazgulami, Ishkashimi, and Bartang, all Iranian languages. Another distinct group is formed by the Yaghnabis, direct descendants of the ancient Sogdians, who live in the Zeravshan River basin.