This is a set of six birdcage or chicken coop windsor side chairs. Today, it is rare to find a large set still in tact. Many sets over the years become broken or divided among family members. This set is in good condition with an older shellac finish. They date around 1800 to 1820 and were made in Pennsylvania. This particular style of windsor chairs was considered a very durable and sturdy design.
Windsor chairs were made from a variety of woods, including: hickory, ash, maple, pine, and poplar. At one time most windsors were painted and have been refinished later usually in the early 20th century. Windsor chairs were painted for several reasons: to unify the appearance of the diverse woods used in their construction, to add decorative flourishes, and if the chairs were used outside, to protect them.
The late 18th and 19th centuries were when the windsor chair developed in America and transformed itself into many different styles. This set of chairs is referred to as chicken coop or birdcage windsors. This is in reference to their cage-like back.
For further references see:
The Windsor Style in America, Charles Santore (Phila. 1992)
The Windsor Chair, Thomas H. Ormsbee (New York, 1962)
American Windsor Chairs, Nancy Goyne Evans (New York 1996)