About St. Clair Welcome Home to ST. CLAIR TERRACE. St. Clair is an apartment located in Washington County, the 21742 ZIP Code, and the Washingtion County Public Schools attendance zone. The Apartment Gallery is a privately owned firm that provides a full menu of services for investors in multi-family and other residential rental real estate. We provide professional management services for over 5,000 apartments and townhomes throughout Pennsylvania, Maryland, and Virginia.