The original part of the Blair–Dunning House is a rectangular brick structure with a stone foundation, two stories tall and covered with a gabled roof.
 It is a linear quadruple-pen structure, measuring far longer east-west than north-south.
 Because the house occupies a hilly lot, the foundation under the front of the house is visible above the surface of the ground.
 Prominent elements of the exterior include large rectangular double-hung windows with limestone sills and lintels, a frieze with cornice, and corbelled chimneys on the eastern and western ends.
 The various elements of the house's design combine to form a structure that mixes the Greek Revival and Federal styles of architecture.

When the house was built, its front door faced north; this situation changed in the late 1860s, when wings were added both to the northern side and to the southern side of the original portion.
 As a result, the size of the house nearly doubled, and its main entrance was moved to the eastern end of the original house.
 Both additions are single-story structures with an individual room that measures 26 by 18 feet (7.9 by 5.5 m).
 Architecturally, they closely resemble the original portion of the house, with brick walls, corbelling, gabled roofs, stone window sills and lintels, and end chimneys.

Inside, the Blair–Dunning House is primarily a wooden building; yellow poplar wood is used throughout the building.
 Among the distinctive elements of the six-room interior are baseboards 18 inches (460 mm) tall, fireplaces in every room with massive mantels, and ceilings 11 feet (3.4 m) high,  and a basement.
The original part of the Blair–Dunning House is a rectangular brick structure with a stone foundation, two stories tall and covered with a gabled roof.  It is a linear quadruple-pen structure, measuring far longer east-west than north-south.  Because the house occupies a hilly lot, the foundation under the front of the house is visible above the surface of the ground.  Prominent elements of the exterior include large rectangular double-hung windows with limestone sills and lintels, a frieze with cornice, and corbelled chimneys on the eastern and western ends.  The various elements of the house's design combine to form a structure that mixes the Greek Revival and Federal styles of architecture.
When the house was built, its front door faced north; this situation changed in the late 1860s, when wings were added both to the northern side and to the southern side of the original portion.  As a result, the size of the house nearly doubled, and its main entrance was moved to the eastern end of the original house.  Both additions are single-story structures with an individual room that measures 26 by 18 feet (7.9 by 5.5 m).  Architecturally, they closely resemble the original portion of the house, with brick walls, corbelling, gabled roofs, stone window sills and lintels, and end chimneys.
Inside, the Blair–Dunning House is primarily a wooden building; yellow poplar wood is used throughout the building.  Among the distinctive elements of the six-room interior are baseboards 18 inches (460 mm) tall, fireplaces in every room with massive mantels, and ceilings 11 feet (3.4 m) high,  and a basement.
Blair–Dunning House