Udvarhely (German: Oderhellen) was an administrative county (comitatus) of the Kingdom of Hungary. Its territory is now in central Romania (eastern Transylvania). The capital of the county was Székelyudvarhely (now Odorheiu Secuiesc).

Udvarhely county shared borders with the counties of Maros-Torda, Csík, Háromszék, Nagy-Küküllő, and Kis-Küküllő. The county lay in the Carpathian Mountains. Its area was 2,938 km around 1910.

Udvarhely county consisted of three former seats of the Székelys: Udvarhelyszék, Bardóc and Keresztúr (the latter two as filial seats of the former). It was formed in 1876, when the administrative structure of Transylvania was changed. In 1920, by the Treaty of Trianon, the county became part of Romania until 1940 when, by the Second Vienna Award, much of its territory was reassigned to Hungary. After the end of World War II it became again part of Romania. Most of its territory lies in the present-day Romanian county of Harghita, with small parts in Mureș (a small part in the west) and Covasna (a small part in the south-east).

Population by mother tongue

Census	Total	Hungarian	Romanian	German	Other or unknown
1880	105,520	94,311 (92.79%)	3,099 (3.05%)	2,322 (2.28%)	1,910 (1.88%)
1890	110,132	103,209 (93.71%)	3,191 (2.90%)	2,131 (1.93%)	1,601 (1,45%)
1900	118,275	112,607 (95.21%)	2,928 (2.48%)	2,225 (1.88%)	515 (0.44%)
1910	124,173	118,458 (95.40%)	2,840 (2.29%)	2,202 (1.77%)	673 (0.54%)

Population by religion

Census	Total	Roman Catholic	Calvinist	Unitarian	Eastern Orthodox	Lutheran	Greek Catholic	Jewish	Other or unknown
1880	105,520	35,050 (33.22%)	36,533 (34.62%)	24,451 (23.17%)	4,121 (3.91%)	2,747 (2.60%)	2,010 (1.90%)	581 (0.55%)	27 (0.03%)
1890	110,132	37,287 (33.86%)	37,826 (34.35%)	25,544 (23.19%)	4,171 (3.79%)	2,777 (2.52%)	1,745 (1.58%)	768 (0.70%)	14 (0.01%)
1900	118,275	41,893 (35.42%)	40,237 (34.02%)	26,614 (22.50%)	4,101 (3.47%)	2,830 (2.39%)	1,387 (1.17%)	1,204 (1.02%)	9 (0.01%)
1910	124,173	45,116 (36.33%)	41,632 (33.53%)	27,567 (22.20%)	4,020 (3.24%)	2,991 (2.41%)	1,508 (1.21%)	1,313 (1.06%)	26 (0.02%)

In the early 20th century, the subdivisions of Udvarhely county were:

Districts (járás)
District	Capital
Homoród	Oklánd (now Ocland)
Parajd (from 1912)	Parajd (now Praid)
Székelykeresztúr	Székelykeresztúr (now Cristuru Secuiesc)
Udvarhely	Székelyudvarhely (now Odorheiu Secuiesc)
Urban districts (rendezett tanácsú város)
Székelyudvarhely (now Odorheiu Secuiesc)