Walgreen Co. (NYSE: WAG), /b/a Walgreens (without an apostrophe), is a leading pharmacy chain, mail service, and pharmacy benefit manager, with specialty pharmacy operations in 49 states, the District of Columbia and Puerto Rico, with 6,614 locations (as of April 30, 2008). Walgreens is one of the two largest drug store chains in the United States. Walgreens states that it serves 5 million customers per day, filled 583 million prescriptions in fiscal 2007, and expects to have 7,000 stores by 2010. Walgreens was founded in Chicago, Illinois, in 1901 and has since expanded throughout the United States. Its headquarters is located in Deerfield, Illinois.