The 1991 Cal Poly Mustangs football team represented California Polytechnic State University, San Luis Obispo as a member of the Western Football Conference (WFC) during the 1991 NCAA Division II football season.
Led by fifth-year head coach Lyle Setencich, Cal Poly compiled an overall record of 4–6 with a mark of 2–3 in conference play, placing fourth in the WFC.
The team was outscored by its opponents 272 to 271 for the season.
The Mustangs played home games at Mustang Stadium in San Luis Obispo, California.
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