The Office of Institutional Research provides data from approximately 1998 onward at their website: https://ir.calpoly.edu/
Records prior to 1998 from the Office of Institutional Research are available in the University Archives.
Historic demographics and enrollment data
University Archives collections include enrollment records starting with the first year of enrollment. Data is divided by gender, ethnicity and race (starting Fall 1973), department, college, year, and other topics. Email firstname.lastname@example.org to request the data.