| 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.