Fairfax Marriott at Fair Oaks is in the Fair Oaks Shopping Center, along with the venue. The address is 11787 Lee Jackson Memorial Highway, Fairfax, VA. There is a booking code included with the invitations (call one of us if you can't find your copy), or you can call the hotel at 888-236-2427 and tell them it's for the Harmon-Stern wedding.
Extended Stay America is also on the same property, at 12055 Lee Jackson Memorial Highway, Fairfax, VA. It's actually right next door to the venue. So this might also be an option.