Because of the Penal Laws which restricted the political, religious and commercial rights of Irish Catholics, O'Conor left his homeland and moved to Spain where his cousins Alexander (Alejandro) and Dominic O'Reilly, were serving as officers in the Spanish Royal Army.

He and Governor Juan María Vicencio de Ripperdá rejected the petition of Antonio Gil Y'Barbo that the settlers could return to their original homes.

To strengthen the protection of Nueva Vizcaya, Coahuila, Sonora, Mexico he decided to expel the Apaches in the region, making war against these peoples in 1775 and 1776.

August 20, 1775 "I, Hugo Oconor, knight of the order of Calatrava, colonel of infantry in His Majesty's armies and commandant inspector of the frontier posts of New Spain Certify that having conducted the exploration prescribed in Article three of the New Royal Regulation of Presidios issued by His Majesty on the tenth of September 1772 for the moving of the company of San Ignacio de Tubac in the Province of Sonora, I selected and marked out in the presence of Father Francisco Garces and Lieutenant Juan de Carmona a place known as San Agustin del Tucson as the new site of the Presidio.

It is situated at a distance of eighteen leagues from Tubac, fulfills the requirements of water, pasture, and wood and effectively closes the Apache frontier.

The designation of the New Presidio becomes official with the signatures of myself, Father Francisco Garces, and Lieutenant Juan de Carmona, at this mission of San Xavier del Bac, on this twentieth day of August of the year 1775."