Fernando De León, colonization manager of De León's colony and patriot leader in the Texas Revolution, the eldest child of Martín and Patricia De León, was born on his father's ranch in Cruillas, Nuevo Santander (now Tamaulipas) in 1798; he was the only De León child born in Mexico. By the time Martín De León petitioned the Mexican government in 1824 to settle forty-one Mexican families on the lower Guadalupe River, Fernando had married María Antonia Galván and had a son. The government of Coahuila and Texas appointed him commissioner in charge of distributing land and issuing titles to the colonists introduced by his father; he employed as his secretary Plácido Benavides. De León was one of the ten principal citizens honored by the name of Guadalupe Victoria's main street, Calle de los Diez Amigos. He settled on his Rancho Escondido, located seven miles north of town on the Guadalupe River, on which were ruins of the presidio that once protected Nuestra Señora del Espíritu Santo de Zúñiga Mission. Legend tells of the padres hiding church valuables when Indians forced them to abandon the site; the treasure was escondido ("hidden"). Appropriately, De León's ranch was the hiding place of many colonists during Indian raids and of John J. Linn's family during the Texas Revolution. María De León's death was the first in the colony, and her son also died while at college in Louisiana. Don Fernando later married Luz Escalera and adopted the two sons of his brother Silvestre De León when the latter was assassinated in 1842. Fernando assumed the responsibilities of his father upon the death of Martín De León in 1833.
Like other members of the De León family, Fernando took up the Texan cause against Antonio López de Santa Anna. In November 1835 he joined his brother-in-law José M. J. Carbajal and Austin colonist Peter Kerr in driving to New Orleans a large herd of livestock, which they exchanged for $35,000 worth of munitions and provisions intended for the colony and the Texas army. The men chartered the schooner Hanna Elizabeth but were intercepted by a Mexican brig and arrested. De León and Carbajal were imprisoned at Brazos de Santiago and later Matamoros until they managed to escape. Although evidence suggests that the supplies still reached the Texans after the patriot ship William Robbins (Liberty) recaptured the Hanna Elizabeth, the three men were never recompensed for their loss.
After his return to Guadalupe Victoria, De León was appointed in February 1836 as aide-de-camp to acting governor James W. Robinson. He assumed command of the local militia as well as the responsibility for provisioning, arming, and "all other things necessary for the support of the army and the protection and the defense of Texas." Although he was ordered to Gonzales, De León was among the first arrested when Gen. José de Urrea occupied Guadalupe Victoria after the battle of Coleto. He was forced to reveal the location of stores of corn, beef, and horses hidden in a ravine at Dimitt's Landing, an act that underlay later charges of disloyalty to Texas. After the Texan victory at San Jacinto, Urrea released De León only upon his promise to expatriate himself and his brothers and return with the retreating army to Mexico, a promise soon renounced. De León was again arrested on charges of treason, however, when the Texas army under Gen. Thomas Jefferson Rusk liberated Guadalupe Victoria. While in custody he was wounded in an assassination attempt, an act reflecting the bitterness of many Anglo-Americans whose creed, according to John J. Linn, "was the total extermination of the Mexican race and the appropriation of their property to the individual use of the exterminators." Though released without trial De León was ostracized and forced to flee with the Carbajal, Benavides, and De León families to Louisiana, abandoning property and possessions valued at hundreds of thousands of dollars. They lived in poverty in New Orleans for about three years before moving to Mexico. Ironically, the De León family was cited as delinquent in paying their 1840 property taxes, over $1,820, to the Republic of Texas.
De León returned about 1844 to reclaim his property and was involved in lawsuits until his death. After recovering only a portion of his ranch and amassing but a few hundred head of cattle, he died at Rancho Escondido in 1853. Francisco Santiago De León, one of his adopted sons, who returned to Mexico about 1852, became the governor of Tamaulipas in 1862 and was assassinated.