Alfonsus, also spelled Alfonso, is of Germanic origin and means "ready for battle". It was introduced into England by way of Normandy after the Norman conquest. In France, it has been popularized by several monarchs from the House of Bourbon who bore the name Alphonse. The name Alfonson is not particularly common in English-speaking countries but has seen some usage throughout history. Notable figures with this name include Alfonso V, the King of Portugal and the Algarves, and Alfonso XIII, the last king of Spain before the Spanish monarchy was abolished in 1931.
The name Alfonson appeared in birth records eight times in the year 1965.