Henri Castro (1786-1861), a naturalized American of French origin, befriended the Republic of Texas and became interested in settling here. In 1842 he was given authority to establish a colony of Europeans in Southwest Texas. He succeeded in obtaining some land here on the Medina, from a 1766 grant made by Chares III of Spain. He recruited 485 families and 457 single men, mostly Alsatians. Using his personal wealth, he cared for the colonists as though they were his children. In 1844 he had the Castroville townsite platted, reserving as his homestead this block next to the courthouse site, in the center of town. He erected a stone dwelling and outbuildings, and planted an experimental garden, to discover crops suited to the locality. Bringing his wife Amelia (Mathias) and their four foster children from France, he lived here permanently. As a moral obligation, he continued to direct the state affairs for his colony, although it had impoverished him.
On the eve of a trip abroad when the Civil War was beginning (1861), Castro and his wife deeded the homestead to their adopted son, Lorenzo. Castro died at Monterrey, Mexico, soon afterward, and was buried there. Lorenzo sold the homestead in 1872.