Costco Wholesale in Frederick, MD is holding an open house on Saturday and Sunday, March 9 and 10, from 11 a.m. to 5 pm. Members and non-members alike are welcome to shop these days only! New Costco members signing up during the event will receive a $10 or $20 Costco Cash Card. Members: bring a friend, and when they sign up for membership, receive a $10 Costco Cash Card. For full details on all offers, please contact us at 301-644-1480.