The Second Guest Block (East portion), located at 142 Queen Street East, is on the south side of Queen Street East in downtown St. Marys. The three storey limestone commercial building was constructed in 1868.

The property was designated by the Town of St. Marys in 1981 for its architectural value or interest under Part IV of the Ontario Heritage Act (By-law 69-1981).

The Second Guest Block (East portion) is part of a continuous limestone commercial block that contributes greatly to the downtown vernacular. Its location and limestone cladding provide visual continuity and add to the distinctive character of the historic downtown. The structure is associated with T.B. Guest, a prominent businessman and an ambitious politician. Guest served as the first Reeve of Blanshard Township, the first Reeve of the village of St. Marys, the first Mayor of the town and as an elected member of the Ontario Legislature representing South Perth. Guest was responsible for building a number of commercial buildings in the downtown core, including this imposing limestone block in 1868.

The Second Guest Block (East portion) is also associated with the Eedy family who operated a local newspaper called the St. Marys Journal Argus from these premises for most of the 20th century. J.W. Eedy came to St. Marys in 1896 from St. Thomas and bought the St. Marys Journal. In 1920, it was amalgamated with a rival weekly journal, the St. Marys Argus, and became the St. Marys Journal Argus. Although the paper is now operating from another downtown location, it retains a strong association with the Second Guest Block (East portion).

The Second Guest Block is considered to be one of the most picturesque storefronts in the Town of St. Marys. Reminiscent of the Classical Revival style, the store features a simple plan with careful proportions composed of large limestone blocks. The recessed entrance, situated to the far right of the storefront, features an attractive wooden transom while the two large display windows occupy the left and sit above handsomely carved wooden mouldings. The facade's second and third storeys display intricate detailing in the large concrete quoins, the raised voussoirs surrounding the windows and the stone lugs below the windows. Also of note is the flat roof, typical of 19th century commercial buildings, which exhibits a cornice with double sets of brackets as supports and a miniature wooden fence atop.