Santa Cruz is a county in southern Arizona, United States.

The river originates in the Canelo Hills in the eastern portion of the county, crosses south into Mexico near the community of Santa Cruz, Sonora, and then bends northwards returning into the United States (and Santa Cruz County) east of Nogales.

Father Eusebio Kino, an Italian explorer and missionary in the service of the Spanish Empire, named the Santa Cruz River–"holy cross" in Spanish–in the 1690s.

In addition, Kino founded several missions to evangelize the different O'odham peoples living along the banks of the Santa Cruz River, including Missions San Cayetano del Tumacácori (1691) and San Gabriel de Guevavi (1691), as well as Los Reyes de Sonoita (1692) near Sonoita Creek.

The ruins of all three of these later missions are now protected by Tumacácori National Historical Park.

Disease, warfare, overwork, and changes in land ownership during Spanish colonization led to the demographic decline of the O'odham peoples of Santa Cruz County.

There are three crossings of the U.S.-Mexico border in Nogales: the Dennis DeConcini Port of Entry (for vehicular and pedestrian traffic); the Nogales-Mariposa Port of Entry (in the western part of the city, for vehicular and pedestrian traffic); and the Morley Gate Port of Entry (for pedestrians only).

16.5% of all households were made up of individuals, and 7.1% had someone living alone who was 65 years of age or older.

Secondary: Elementary: The population ranking of the following table is based on the 2010 census of Santa Cruz County.

Following the trends seen in majority Hispanic counties across the United States, Joe Biden defeated Donald Trump with 67.1% of the popular vote in the county, a slightly lower margin than Hillary Clinton's 71.1% vote share in 2016.

Elizabeth Gutfahr, former elected county treasurer who confessed to embezzling more than $38 million between 2012 and 2024.