Idelfonso (Idelfonsus) is a Spanish given name, ultimately from Gothic Hildefuns, the name of 7th-century saint Ildephonsus of Toledo. People Ildefons Cerdà, Spanish urban planner Ildefonso Falcones, Spanish author Ildefonso Lima, Andorran footballer Ildefonso Puigdendolas, Spanish military officer Ildefonso Santos, Filipino educator and poet Ildefonso Santos Jr., Filipino architect Ildefonso Schuster, archbishop of Milan, Italy Konstanty Ildefons Gałczyński, Polish writer and poet Places Ildefonso Islands, group of islands in Chile. San Ildefonso Ixtahuacán, a municipality in Guatemala. San Ildefonso Peninsula, a peninsula in the Philippines. San Ildefonso Pueblo, New Mexico, a census-designated place in the USA. San Ildefonso, Bulacan, a municipality in the Philippines. San Ildefonso, Ilocos Sur, a municipality in the Philippines. San Ildefonso, San Vicente, a municipality in El Salvador. San Ildefonso, a town in Spain. Santo Ildefonso, a parish in Portugal. Treaty of San Ildefonso First Treaty of San Ildefonso of 1777 between Spain and Portugal. Second Treaty of San Ildefonso of 1796 between Spain and France, allying the two nations. Third Treaty of San Ildefonso of 1800 between Spain and France, by which Spain returned Louisiana to France. Other Convent of St. Ildefonso, a book by Regina Marie Roche. , a British Royal Navy ship. Palacio Real de la Granja de San Ildefonso, a palace in the Spanish province of Segovia. Church of Saint Ildefonso, an 18th-century church in Porto See also Alfonso Alfonso (disambiguation)