Monterey Jack (sometimes shortened simply to Jack cheese) is an American semihard cheese, customarily white, made using cow's milk. It is commonly sold by itself, or mixed with Colby to make a marbled cheese known as Colby-Jack (or Co-Jack). Cheddar-Jack and Pepper Jack varieties are also available.In its earliest form, Monterey Jack was made by the Mexican Franciscan friars of Monterey, California, during the 19th century. Californian businessman David Jack sold the cheese commercially.