The 2004 Cal Poly Mustangs football team represented California Polytechnic State University during the 2004 NCAA Division I-AA football season. Cal Poly competed as a charter member of the new Great West Football Conference (GWFC). They had previously been a Division I-AA Independent. The Mustangs were led by fourth-year head coach Rich Ellerson and played home games at Mustang Stadium in San Luis Obispo, California. The team finished the season as champion of the GWFC, with a record of nine wins and two losses (9–2, 4–1 GWFC). Overall, the team outscored its opponents 336–183 for the season.