Ourinhos is a Brazilian municipality in the interior of the state of São Paulo. Located west of the state capital, it is approximately 370 km away. Covering an area of 296 km² (114 sq mi), its population according to the 2022 Brazilian census by the Brazilian Institute of Geography and Statistics (IBGE) was 103,970, making it the 76th most populous in São Paulo. It is 994 km from Brasília, the federal capital.

The municipality was emancipated from Salto Grande in the 1910s, and its name refers to the former municipality of Ourinho, now Jacarezinho, in the state of Paraná. Currently, it consists of the city of Ourinhos, with its seat being its only district, further subdivided into approximately 120 neighborhoods. It is also one of the main cities in the region, with commerce as its primary economic activity. In agriculture, the cultivation of sugarcane, soybean, and maize stands out.

The municipality also boasts a rich cultural tradition, encompassing handicrafts, theater, music, and sports. The city is notable for events often organized by the Ourinhos city hall, sometimes in partnership with local businesses. One of the main events is the Ourinhos Agricultural and Industrial Fair, held annually in June and considered one of the largest events of its kind in the country.

Until the late 19th century, the area that is now the municipality of Ourinhos was a pristine forest, inhabited by the Kaingang Indians. During this period, monocultures of coffee and cotton reached the hinterlands along the Paranapanema River, accompanied by the onset of Italian immigration, which rapidly populated the area. This led Jacinto Ferreira de Sá, originally from Santa Cruz do Rio Pardo, to acquire a vast tract of land from Escolástica Melchert da Fonseca. He subdivided the central portion and donated land for the construction of a school, an administrative headquarters, and a Methodist church.

In 1906, a small settlement with a limited number of houses began to form. In 1908, a railway post was established, which, four years later, was transformed into a railway station belonging to the Sorocaba Railway. The station served as a transfer point for passengers heading to the neighboring settlement of Ourinhos (now Jacarezinho, Paraná). From this time onward, the future city’s development was driven by the fertility of its lands and its advantageous geographical position, making it a strategic economic location due to its connection with northern Paraná and its position between Assis and Avaré, key cities in the Paranapanema Valley. The small settlement became a district under Salto Grande de Paranapanema in 1915. Three years later, it was elevated to the status of municipality on 13 December 1918, with its official establishment on 20 March 1919.

It was elevated to a district under the name Ourinhos by State Law No. 1484 on 13 December 1915, belonging to the municipality of Salto Grande. It was then elevated to municipality status under the same name by Law No. 1618 on 13 December 1918, separated from Salto Grande. It consisted of the seat district, with its establishment occurring on 20 March 1919. By State Decree-Law No. 9073 of 31 March 1938, the Municipality of Ourinhos was part of the sub-district of Salto Grande, within the Salto Grande judicial district. Under the framework established by State Decree No. 9775 of 30 November of the same year, it became the sole sub-district of the Ourinhos judicial district.

The name "Ourinhos" was used even before its political emancipation. A 1908 map shows a city named Ourinho (singular) in Paraná, where Jacarezinho now stands. In fact, the Paraná Ourinho was also called Nova Alcântara, chosen by its founder, Antônio Alcântara da Fonseca, a miner who settled there in 1888. State Law No. 352 of 2 April 1900 established that Nova Alcântara (or Ourinho) and the Jacarezinho police district be incorporated into the Jacarezinho sub-district, with the appointment of a judge and deputy prosecutor. Law No. 525 of 9 March 1904 created the Jacarezinho judicial district, effectively dissolving the Paraná Ourinho, though maps continued to use the old name for some time. The Sorocaba Railway formalized the São Paulo Ourinhos, which inherited the name through oral tradition. Thus, Ourinhos was already referred to by this name regionally, as Ourinho was sometimes called Nova Alcântara, causing confusion among residents who often referred to the current Ourinhos even before its official designation. Like many Brazilian cities, Ourinhos was already a city in practice before its official political emancipation.

With the resumption of the railway and deforestation, fertile lands facilitated coffee cultivation for export, which was highly profitable for landowners at the time. Concurrently, merchants and professionals from various regions arrived, contributing to the municipality’s growth and development. During this period, immigrants from Japan, Italy, and other countries were attracted to Ourinhos, primarily to cultivate lands along the railway. Another railway, the São Paulo-Paraná Railway, built in 1922, connected São Paulo and Paraná, making Ourinhos a significant economic hub and junction.