Hermosillo (Latin American Spanish: [eɾmoˈsiʝo] ^ⓘ), formerly called Pitic (as in Santísima Trinidad del Pitic and Presidio del Pitic), is a city in the center of the northwestern Mexican state of Sonora. It is the municipal seat of the Hermosillo municipality, the state's capital and largest city, as well as the primary economic center for the state and the region. As of 2020, the city has a population of 936,263, making it the 18th largest city in Mexico. The recent increase in the city's population is due to expanded industrialization, especially within the automotive industry.

In 2013 and 2018, Hermosillo was ranked as one of the top cities in Mexico for quality of life by the Strategic Communications Cabinet of the Mexican Federal Government.

Hermosillo was also ranked in 2016 as the seventh most competitive city in the country according to the Mexican Institute for Competitiveness (IMCO), based on factors such as its economic diversification, geographical location, access to education, government, innovation and international relations. The major manufacturing sector has been the production of automobiles since the 1980s. It is one of the richest cities in Mexico by GDP per capita.

Hermosillo has a subtropical hot desert climate (BWh). Temperatures have been as high as 49.5 °C (121.1 °F) in the summer months, making it one of the hottest cities in the country.

Evidence from a site called the San Dieguito Complex, located in the El Pinacate Zone, suggests the area has been inhabited by humans for about 3,000 years. Evidence of agriculture dates back 2,500 years. In the pre-Hispanic era, this area was inhabited by the historic Seri, Tepoca, and Pima peoples.

The first encounter between the Spanish and the indigenous peoples of the area occurred in the middle of the 16th century, when European explorers came in search of gold. The Spanish explorers were followed by Jesuit missionaries in the state of Sonora around 1614. Eusebio Francisco Kino arrived in 1687, founding a mission in nearby Cucurpe. The present-day states of Sonora and Sinaloa were loosely organized as the provinces of Sonora, Ostimuri, and Sinaloa.

In 1700, three small Spanish villages were founded in what is now the outskirts of Hermosillo: Nuestra Señora del Pópulo, Nuestra Señora de Los Angeles, and la Santísima Trinidad del Pitic. The native peoples here soon became hostile to the colonists and repeatedly drove them out in the early 18th century. In 1716, the Spanish offered irrigated lands for farmers to the native peoples, who agreed to abide by Spanish law. Around 1726, a fort named the Presidio of Pitic was constructed to stop the domination of this area by the natives, especially the Seri. However, the situation remained contentious. The first church was not built until 1787, and the first formal parish was not established until 1822.

During the Mexican War of Independence, Sonora and the town of Pitic stayed loyal to the Spanish Crown. Local general Alejo García Conde defeated insurgent José María González Hermosillo, who had been sent by Miguel Hidalgo y Costilla. Following independence from Spain, in 1825 the village of Pitic was made the seat of the department of the same name. In 1828, the settlement changed its name to Hermosillo to honor the insurgent leader José María González de Hermosillo.