The first modern population census on the territory of Slovenia was conducted on 31 October 1857. Within the then Austria-Hungary population censuses were also conducted in 1869, 1880, 1890, 1900 and 1910 (the census reference day was 31 December). Between the two world wars only two censuses were conducted (on 31 January 1921 and on 31 March 1931). After World War II – within the then Yugoslavia – six more censuses were conducted: 15 March 1948, 31 March 1953, 31 March 1961, 31 March 1971, 31 March 1981 and 31 March 1991. The last census – conduced on 31 March 2002 – was the first population census in independent Slovenia. At the 1971–2002 censuses data on dwellings were also collected, at the 1981 and 1991 censuses also data on households with agricultural holdings and at the 2002 census for the first time also data on buildings.

Census data collected before World War II show de facto population, i.e. population actually living on the territory of Slovenia on the census date. Census data collected after World War II (1948–1991) took into account population with permanent residence in Slovenia (de jure). Taken into account were people who declared that they have permanent residence in the place of enumeration, irrespective of whether they were temporarily absent at the time of the census. Temporarily absent people were those who were absent for a short time and also those who were working abroad and family members who were living with them abroad (migrant workers), irrespective of the duration of their work or stay abroad.