On November 12, 1923, Officer Allen was off duty when it was reported to him that a neighbor was stringing illegal radio wire to a residence. Officer Allen went to the residence to investigate, and located the neighbor and radio wire. Officer Allen picked up one end of the radio wire, which then came in contact with an overhead power line. Officer Allen was accidentally electrocuted and immediately died as a result. Officer Allen left a wife and a 4-day-old daughter.

Officer William D. Allen is the earliest known U.S. Park Police officer to die in the line of duty. His name will be engraved on panel 55E line 27.