The regions are subdivided into districts (wilaya in Swahili). There were 129 districts in 2003. Subordinate to the districts are divisions, under the divisions are wards, and under the wards (except in urban districts) are villages.
The distinction between Tanzania Mainland and Tanzania Zanzibar, corresponding to the two countries that merged in 1964, is still observed.
- Kagera includes Bumbiri, Ikusa, Bukerebe, Nabuyongo, and other islands in Lake Victoria.
- Lindi includes Songa Manara Island in the Indian Ocean.
- Mara includes Lukuba Island and a few other small islands in Lake Victoria.
- Mwanza includes Ukerewe, Rubondo, Ukara, Maisome, Kome, Irugwa, and other islands in Lake Victoria.
- Pemba North and Pemba South share Pemba Islands.
- Pwani includes Mafia Island in the Indian Ocean.
- Tanga includes Mwambawamba Island and other small islands in the Pemba Channel.
- Zanzibar North, Zanzibar South and Central, and Zanzibar West share Zanzibar Island.
- Tumbatu Island is in Zanzibar North; Uzi and Pungume Islands are in Zanzibar South and Central.
The UN LOCODE page for Tanzania lists locations in the country, some of them with their latitudes and longitudes, some with their ISO 3166-2 codes for their subdivisions. This information can be put together to approximate the territorial extent of subdivisions.
Origins of names:
- Dar es Salaam: Arabic dar as-salam: home of peace
- Iringa: Hehe lilinga: fort
- Tabora: Nyamwezi matoborwa: sweet potatoes
- Zanzibar: from an Arabic word for blacks
Divisions of Tanganyika in 1922 were: Arusha, Bagamoyo, Bukoba, Daressalam, Dodoma, Iringa, Kilwa, Kondoa-Irangi, Lindi, Mahenge, Morogoro, Moshi, Mwanza, Pangani, Rufiji, Rungwe, Songea, Tabora, Tanga, Ufipa, Ujiji, and Usambara. Numerous changes occurred between then and independence. The situation as of 1948, according to source , was:
- ~1961: Dar es Salaam province split from Eastern; West Lake province split from Lake.
- 1964-04-26: Tanganyika and Zanzibar merged. Tanzania now consisted of these twelve provinces:
|Dar es Salaam||128,742||1,393||Dar es Salaam||Coast (part)|
|Eastern||955,828||107,630||Dar es Salaam||Coast (part), Morogoro|
|Lake||1,731,794||107,711||Mwanza||Mara, Mwanza, Shinyanga (part)|
|Northern||772,434||85,374||Arusha||Arusha, Kilimanjaro (part)|
|Southern Highlands||1,030,269||119,253||Mbeya||Iringa, Mbeya (part)|
|Tanga||688,290||35,750||Tanga||Kilimanjaro (part), Tanga|
|West Lake||514,431||28,388||Bukoba||West Lake|
|Western||1,062,598||203,068||Tabora||Kigoma, Mbeya (part), Shinyanga (part), Tabora|
|Zanzibar||165,253||1,658||Zanzibar||Zanzibar Rural, Zanzibar West|
- ~1966: Tanzania reorganized into twenty regions.
- ~1967: Zanzibar Shambani (Rural) region split into Zanzibar Shambani North and Zanzibar Shambani South, which later became Zanzibar North and Zanzibar South and Central.
- ~1971: Rukwa region created from parts of Mbeya and Tabora.
- 1972-07-01: Lindi region split from Mtwara.
- 1974-01-01: Dar es Salaam region split from Coast.
- ~1982: Name of Coast region changed to Pwani; Pemba region split into Pemba North and Pemba South.
- ~1984: Name of West Lake region changed to Kagera.
- ~2002-05: Manyara region split from Arusha (former HASC code TZ.AR, FIPS code TZ01) (Sources -). All sources agree that Manyara contains Babati, Hanang, Kiteto, and Mbulu districts. That's all that source  seems to list. Source  adds Manyara and Simanjiro districts. If I follow the German text correctly, source  also says that the southern part of Monduli district was annexed to Babati district. Source  lists adds Simanjiro district and Babati town to the four.
- 2012-03-02: Government Notice No. 72 took effect. Geita region (capital Geita) formed by taking Bukombe district from Shinyanga region, Chato from Kagera, and Geita from Mwanza; Katavi region (capital Mpanda) formed by taking Mpanda district from Rukwa region; Njombe region (capital Njombe) formed by taking Ludewa, Makete, and Njombe districts from Iringa region; Simiyu region (capital Bariadi) formed by taking Bariadi, Meatu, and Maswa districts from Shinyanga region, and the newly created Busega district from Mwanza. The former HASC codes of the diminished regions were TZ.IR (Iringa), TZ.KR (Kagera), TZ.MW (Mwanza), TZ.RK (Rukwa), and TZ.SH (Shinyanga).
Other names of subdivisions:
- Dar es Salaam: Daressalam (German)
- Kagera: West Lake (obsolete); Ziwa Magharibi (Swahili-obsolete)
- Pemba North: Kaskazini Pemba (Swahili); Pemba Septentrional (Spanish)
- Pemba South: Kusini Pemba (Swahili); Pemba Meridional (Spanish)
- Pwani: Coast (obsolete)
- Zanzibar: Sansibar (German); Zanzíbar (Spanish)
- Zanzibar North: Kaskazini Unguja (Swahili); North Unguja, Zanzibar Rural North, Zanzibar Shambani North (variant); Zanzibar Septentrional (Spanish)
- Zanzibar South and Central: Kusini Unguja (Swahili); South Unguja, South Zanzibar, Unguja South & Central, Zanzibar Rural South, Zanzibar Shambani South (variant); Zanzibar Meridional/Central (Spanish)
- Zanzibar West: Mjini Magharibi (Swahili); Unguja Town & West, Urban West, Zanzibar Mjini, Zanzibar Urban, Zanzibar Urban/West (variant); Zanzibar Occidental (Spanish)
|Dar es Salaam||356,286||843,090||1,360,850||2,487,288||4,364,541|
|Zanzibar South and Central||39,087||51,749||70,313||94,244||115,588|
Data for 1967 to 1988 from source , a Tanzanian government website. Manyara was included in Arusha in 1967 and 1978 figures. Apparently, in all other cases, data are proleptic to the boundaries as of 2002. Data for 2002 and 2012 from source , proleptic to 2012 boundaries.