The By-laws of Dairy Institute provide for three membership groups:

Dairy Institute currently has 35 member companies who operate plants in California and which collectively account for approximately 80% of all fluid milk products, cultured and frozen products, and hard cheese produced in the state. Dairy Institute members also manufacture substantial quantities of butter and nonfat dry milk powder. Members include proprietary and cooperative processors of varying sizes, vertically-integrated grocery chains operating their own milk plants and producer-distributors.

There are currently 6 Affiliate member companies representing non-processing distributors, out-of-state processors, and other organizations related to the California dairy industry. Affiliate members do not participate in the governance of Dairy Institute but receive all services provided to Processor members.

There are 31 Associate member companies that include packaging companies; ingredient suppliers, and equipment manufacturers. Associate members do not participate in the governance of Dairy Institute nor do they receive all services provided to the other member groups. Associate members are invited to participate in the annual spring meeting. All members are elected by the Board of Directors.