Green Mountain Coffee Roasters and Starbucks is who makes coffee for Costco.
Although other companies also make some of the coffee for Costco, but Starbucks and Green Mountain Coffee Roasters are the two most common coffee manufacturers for Costco.
Starbucks also historically produced some of the Kirkland Signature whole bean coffee, like the House Blend and Espresso Blend coffee.
Although some recent changes have also seen the removal of the Starbucks branding from some of the products, which also suggests a potential shift in the manufacturing partners.
And Green Mountain Coffee Roasters is also known to produce the Kirkland Signature K-Cups for the Keurig machines.
Starbucks does produce some of the Kirkland branded coffee beans although Starbucks branding has been removed from some of the Costco coffee products.
Both Starbucks and Green Mountain coffee manufacturers are confirmed to make coffee for Costco but there are some other unknown companies that make Costco coffee as well.
Both the Kirkland whole bean espresso blend and its decaf blend coffee are, or at least were, supplied by Starbucks, but Costco appears to have used another company for its Colombian coffees (including the “Colombian Supremo” variety).
California-based Rogers Family Co. has been named as one supplier of this coffee.