San Agustín de la Isleta Mission, founded in 1613, was a Spanish Mission in what is now Bernalillo County, New Mexico, United States. It was …San Agustín de la Isleta Mission, founded in 1613, was a Spanish Mission in what is now Bernalillo County, New Mexico, United States. It was a religious outpost established by Spanish Catholic Franciscans, to spread Christianity among the local Native Americans.