| Name | William Foss | 
| Agency | Libertyville Fire Department | 
| Rank | Assistant Chief | 
| Type of Firefighter | Paid-On-Call (POC) | 
| Age Range | [Unknown] | 
| Sex | Male | 
| Date of Birth | 0/0/0 | 
| Date of Death | 10/12/1971 | 
| Cause of Death | Stress/Overexertion | 
| Nature of Death | Heart attack | 
| Attribute of Death | [not applicable] | 
| Type of Duty | Post-incident | 
| Incident Name | N/A | 
| Incident City | Libertyville | 
| Incident State | IL | 
| Incident Date | 10/12/1971 | 
| Incident Location | [Unknown] | 
| Incident Attribute | [Not applicable] | 
On October 12, 1971, Assistant Chief William Foss of the Libertyville Fire Department suffered a fatal heart attack, his second heart attack while on duty with the Libertyville Fire Department. Foss had suffered his first heart attack during a training exercise a few years earlier, and doctors had cleared him to return to active duty.
Foss served with the Libertyville Fire Department as a volunteer firefighter from March 1948 to November 1950. He rejoined the department in September 1952 and remained a paid-on-call member until his death nineteen years later.