International standard ISO 3166-2 has always listed what I call the secondary subdivisions of Taiwan as if they were primary. It uses the name "Taiwan, Province of China" for the area covered. That is a slight misnomer, because the ROC controls part of Fukien, which all parties seem to agree is a separate province from Taiwan. Those of us with memories of 1960 may recall that a big issue in the televised debates between Nixon and Kennedy was what to do about Quemoy and Matsu, the main islands of Fukien controlled by the ROC.

"Geopolitical Entities, Names, and Codes, Edition 2" (GENC), a U.S. standard that's supposed to correspond to ISO 3166-2, was issued on 2014-03-31. It gives codes for the two counties in Fukien province: TW-KIN for Kinmen and TW-LIE for Lienkiang. Its codes for all the other municipalities match the ISO codes. After the ISO update of 2015-11-27, the codes, statuses, and names given in the two standards match perfectly except for the code for New Taipei. GENC still uses the old code, TW-TPQ.

The draft standard (1996) listed two provinces, two special municipalities, sixteen districts, and five municipalities. There was an unexplained overlap: Taiwan province actually included the territory of all sixteen districts and five municipalities. Each division was given a three-letter code. Whenever possible, the IATA airport code for the division's main city was used; elsewhere, the ISO working group assigned arbitrary three-letter abbreviations. There were some ambiguous codes. TNN represented both Tainan district and Tainan municipality, which are actually disjoint but adjacent entities on the secondary level. KHH represented both Kaohsiung special municipality and Kaohsiung district, which are not only disjoint but on different levels. The final standard (1998) lists the same subdivisions, except that the two provinces were dropped, and the name and code of one municipality were changed from Chilung (CHI) to Keelung (KEE). (Chilung and Keelung are alternate romanizations of the same Chinese name.) Dropping the two provinces eliminated the overlap of Taiwan province, but left the ROC-administered part of Fukien province, consisting of Quemoy, Matsu, and other islands, unrepresented. There were still duplicate codes, until ISO 3166-2 Newsletter number I-4 was issued on 2002-12-10. It modified the codes for six of the districts, eliminating duplicate codes. On 2015-11-27, ISO issued more updates, deleting three districts, adding the two districts of Fukien province, changing the code for New Taipei from TW-TPQ to TW-NWT, and changing the status of four subdivisions.

Update 2 to "Geopolitical Entities and Codes" was published on 2010-11-30. For Taiwan, it revoked the province codes and replaced them by a set of county and municipality codes, shown below under "FIPS." Update 4, issued on 2011-04-30, revoked three of the codes that were issued in Update 2: TW11 for Kaohsiung county, TW20 for Taichung county, and TW22 for Tainan county. It also changed the name and status of Taipei county to New Taipei municipality.

County	Typ	HASC	ISO	FIPS	Population	Area(km.²)	Capital	Postcode
Changhwa	c	TW.TA.CG	CHA	TW05	1,226,420	1,074	Changhwa	500-530
Chiayi	c	TW.TA.CH	CYQ	TW07	492,981	1,904	Chiayi	602-625
Chiayi City	m	TW.TA.CS	CYI	TW06	267,651	60	Chiayi	600
Hsinchu	c	TW.TA.HH	HSQ	TW09	522,163	1,428	Hsinchu	302-315
Hsinchu City	m	TW.TA.HS	HSZ	TW08	476,273	104	Hsinchu	300
Hualien	c	TW.TA.HL	HUA	TW10	309,941	4,629	Hualien	970-983
Ilan	c	TW.TA.IL	ILA	TW26	426,975	2,144	Ilan	260-272
Kaohsiung City	s	TW.KH.KS	KHH	TW02	2,777,384	2,949	Kaohsiung	800-852
Keelung City	m	TW.TA.CL	KEE	TW12	381,809	133	Keelung	200-206
Kinmen	c	TW.FK.KM	KIN	TW13	57,221	152		890-896
Lienkiang	c	TW.FK.LK	LIE	TW14	14,604	29		209-212
Miaoli	c	TW.TA.ML	MIA	TW15	530,339	1,820	Miaoli	350-369
Nantou	c	TW.TA.NT	NAN	TW16	460,869	4,106	Nantou	540-558
New Taipei City	s	TW.NT.TP	NWT	TW23	4,054,467	2,053	Panchiao	207-208, 220-253
Penghu	c	TW.TA.PH	PEN	TW17	86,967	127	Makung	880-885
Pingtung	c	TW.TA.PT	PIF	TW18	801,012	2,776	Pingtung	900-947
Taichung City	s	TW.TG.TU	TXG	TW19	2,731,056	2,215	Taichung	400-439
Tainan City	s	TW.TN.TI	TNN	TW21	1,840,257	2,192	Tainan	700-745
Taipei City	s	TW.TP.TC	TPE	TW03	2,655,515	272	Taipei	100-116
Taitung	c	TW.TA.TT	TTT	TW24	201,039	3,515	Taitung	950-966
Taoyuan	s	TW.TA.TY	TAO	TW25	2,190,342	1,221	Taoyuan	320-338
Yunlin	c	TW.TA.YL	YUN	TW27	618,581	1,291	Touliu	630-655
22 divisions					23,123,866	36,192
Typ: c=county, m=municipality, s=special municipality HASC: Hierarchical administrative subdivision codes. Middle two letters indicate the province. For key, see Taiwan Provinces page. ISO: Codes from ISO 3166-2. For full identification in a global context, prefix "TW-" to the code (ex: TW-HSQ represents Hsinchu county). FIPS: Codes from FIPS PUB 10-4. Population: 2010-12-31 census. Postcode: Taiwan uses five-digit postal codes in nnn-nn format. The first three digits indicate the county.

Change history:

1. The Encyclopædia Britannica World Atlas, 1957 edition shows Taiwan subdivided into sixteen counties and five municipalities. It does not include any territory in Fukien province, where Taiwan holds a number of offshore islands. In the list below, I have changed some county names to a more modern spelling, and corrected some evident errors in the data.
2. The Atlas claims to include data from the 1951 and 1953 censuses, but according to the U.S. Census Bureau's compilation, the first modern census of Taiwan was taken in 1956.

County	Type	Population	Area(km.²)	Area(mi.²)
Changhwa	cn	704,471	1,062	410
Chiayi	cn	542,042	1,951	753
Hsinchu	cn	349,879	1,481	572
Hualien	cn	178,932	4,629	1,787
Ilan	cn	262,441	2,137	825
Kaohsiung	cn	464,317	2,833	1,094
Kaohsiung City	mu	282,360	113	44
Keelung City	mu	151,927	132	51
Miaoli	cn	349,339	1,820	703
Nantou	cn	308,205	4,106	1,586
Penghu	cn	81,378	127	49
Pingtung	cn	487,546	2,776	1,072
Taichung	cn	480,381	2,051	792
Taichung City	mu	202,969	163	63
Tainan	cn	626,059	2,004	774
Tainan City	mu	226,363	175	68
Taipei	cn	592,118	2,258	872
Taipei City	mu	540,971	67	26
Taitung	cn	121,415	3,515	1,357
Taoyuan	cn	346,466	1,267	489
Yunlin	cn	531,169	1,291	498
Totals		7,830,748	35,958	13,885
Type: cn = county, mu = municipality Population: 1951

1. ~1952: Yangmingshan municipality split from Taipei county. This change was apparently reversed not long afterward.
2. Chiayi City and Hsinchu City must have been split from their respective counties between ~1953 and ~1970.
3. 1967: Taipei municipality split from Taiwan province to become Taipei special municipality.
4. 1979: Kaohsiung municipality split from Taiwan province to become Kaohsiung special municipality.
5. ~1989: Capital of Taiwan province moved from Taichung to Chung-hsing-hsin-tsun.
6. ISO 3166-2 originally (and inadvertently) assigned some duplicate codes. Chiayi county and municipality were both CYI, Hsinchu was HSZ, Kaohsiung was KHH, Taichung was TXG, Tainan was TNN, and Taipei was TPE. Newsletter number I-4, dated 2002-12-10, changed the codes for those six counties, to eliminate the duplicate codes. The new codes are shown in the table below. Even with the revisions, some of the ISO province codes were duplicates of some of the ISO county codes.

County	Typ	HASC	ISO	FIPS	Pop-2000	Pop-1990	Area(km.²)	Capital	Postcode
Changhwa	c	TW.TW.CG	CHA	TW05	1,255,332	1,205,091	1,074	Changhwa	500-530
Chiayi	c	TW.TW.CH	CYQ	TW07	552,749	534,761	1,902	Chiayi	602-625
Chiayi City	m	TW.TW.CS	CYI	TW06	266,126	252,371	60	Chiayi	600
Hsinchu	c	TW.TW.HH	HSQ	TW09	451,316	370,970	1,428	Hsinchu	302-315
Hsinchu City	m	TW.TW.HS	HSZ	TW08	395,746	342,015	104	Hsinchu	300
Hualien	c	TW.TW.HL	HUA	TW10	327,064	336,890	4,629	Hualien	970-983
Ilan	c	TW.TW.IL	ILA	TW26	444,950	436,600	2,144	Ilan	260-272
Kaohsiung	c	TW.TW.KH	KHQ		1,262,969	1,132,195	2,793	Fengshan	814-852
Kaohsiung City	s	TW.KH.KC	KHH	TW02	1,493,806	1,380,663	154	Kaohsiung	800-813
Keelung City	m	TW.TW.CL	CHI	TW12	387,504	348,586	133	Keelung	200-206
Kinmen	c	TW.FK.KM		TW13	56,275	81,479	153		890-896
Lienkiang	c	TW.FK.LK		TW14	17,775	25,975	29		209-212
Miaoli	c	TW.TW.ML	MIA	TW15	534,366	526,181	1,820	Miaoli	350-369
Nantou	c	TW.TW.NT	NAN	TW16	487,398	515,167	4,106	Nantou	540-558
Penghu	c	TW.TW.PH	PEN	TW17	83,214	105,848	127	Makung	880-885
Pingtung	c	TW.TW.PT	PIF	TW18	872,902	875,330	2,776	Pingtung	900-947
Taichung	c	TW.TW.TH	TXQ		1,510,480	1,285,029	2,051	Fengyuan	411-439
Taichung City	m	TW.TW.TG	TXG	TW19	989,047	772,828	163	Taichung	400-408
Tainan	c	TW.TW.TA	TNQ		1,120,394	1,022,203	2,016	Hsinying	710-745
Tainan City	m	TW.TW.TN	TNN	TW21	725,985	672,907	176	Tainan	700-709
Taipei	c	TW.TW.TP	TPQ	TW23	3,722,082	3,065,779	2,053	Panchiao	207-208, 220-253
Taipei City	s	TW.TP.TC	TPE	TW03	2,624,257	2,760,475	272	Taipei	100-116
Taitung	c	TW.TW.TT	TTT	TW24	204,919	249,088	3,515	Taitung	950-966
Taoyuan	c	TW.TW.TY	TAO	TW25	1,808,833	1,377,934	1,221	Taoyuan	320-338
Yunlin	c	TW.TW.YL	YUN	TW27	705,440	717,263	1,291	Touliu	630-655
25 divisions					22,300,929	20,393,628	36,178
Typ: c=county, m=municipality, s=special municipality HASC: Hierarchical administrative subdivision codes. Middle two letters indicate the province. For key, see Taiwan Provinces page. ISO: Codes from ISO 3166-2. For full identification in a global context, prefix "TW-" to the code (ex: TW-TXQ represents Taichung county). FIPS: Codes from FIPS PUB 10-4. Pop-2000: 2000-12-16 census Pop-1990: 1990-12-16 census Postcode: Taiwan uses five-digit postal codes in nnn-nn format. The first three digits indicate the county.

1. 2010-12-25: Kaohsiung county merged with Kaohsiung special municipality; Taichung special municipality formed by merging Taichung county with Taichung provincial city; Tainan special municipality formed by merging Tainan county with Tainan provincial city; Taipei county renamed and status changed to New Taipei special municipality.
2. 2014-12-25: Status of Taoyuan changed from county to special municipality.

Other names of subdivisions:

1. Changhwa: Changhua (variant)
2. Chiayi: Chiai (variant)
3. Hualien: Hwalien (variant)
4. Ilan: Yilan (variant)
5. Keelung: Chilung, Keelong (variant)
6. Kinmen: Chinmen, Kingmen, Quemoy (variant)
7. Lienkiang: Lienchiang, Lienkian, Matsu (variant)
8. New Taipei City: Taipei [county] (obsolete); Xinbei (Chinese)
9. Yunlin: Yüanlin (variant)

Sources:

1. [1] 2000 Population and Housing Census (retrieved from http://www.dgbas.gov.tw/census~n/six/lue5/census_p&h&E.htm on 2004-10-14).
2. [2] 2001 Preliminary Report (Statistics Table) (retrieved from http://www.dgbasey.gov.tw/census~n/two/eh/e61/13/A1.htm on 2004-10-14).
3. [3] Spreadsheet (retrieved from http://www.dgbas.gov.tw/dgbas03/bs2/92chy/table/A101.xls on 2004-10-14)
4. [4] Taiwan Magazine One (retrieved from http://www.twmone.com/business/statistique/recensement.php3 on 2004-10-14)
5. [5] 2010 Population and Housing Census , County/City Report (retrieved 2013-09-25).