18th Separate Company Armory is a historic National Guard armory building located at Glens Falls, Warren County, New York. It is a brick and stone castle-like structure built in 1895, designed to be reminiscent of medieval military structures in Europe. It was designed by State Architect Isaac G. Perry. It is a monumental rectangular brick and stone structure covered by hipped slate roofs. It has a large drill hall. The building features a crenelated tower and narrow recessed windows with stone lintels. It was added to the National Register of Historic Places in 1984.