[5] Yldefonso joined 57th Infantry Regiment of the Philippine Scouts of the United States Army in 1922 upon turning 18 years old.

[7] During World War II, Yldefonso fought against the Japanese in Bataan as part of the Philippine Scouts, reaching the rank of lieutenant.

[10] Yldefonso was married to Manuela Ella in 1925 with whom he had six children:[5] Porfirio, Emilio, Felipe, Norma, Herminia, and Carmelito.

[10] In 2006, the municipal government of Piddig unveiled a monument in Yldefonso's honor for his feats in swimming and World War II.

[7] His daughter, Norma, competed at the 2nd Asian Games held in Manila, Philippines and won a silver medal in the 100m butterfly event.