Question: What is the square footage of this mansion in Duluth, Minnesota, operated by the University of Minnestoa Duluth as a historic house museum, indelibly linked with the Congdon name?

Context paragraphs:
Pequotsepos Manor: Pequotsepos Manor, known formally as Denison Homestead, is a historic house museum at 120 Pequotsepos Road in Mystic, Connecticut.  The house was built in 1717 and added to the National Register of Historic Places on June 15, 1979.  It is now a historic house museum operated by the Denison Society.

Simon Cameron House: The Simon Cameron House, also known as John Harris Mansion and the Harris-Cameron Mansion, is a historic house museum at 219 South Front Street in Harrisburg, Pennsylvania.  Built in 1766 and frequently extended and altered, it is one of Harrisburg's oldest buildings, and is nationally notable as the summer residence of Simon Cameron (1799-1889), an influential Republican Party politician during and after the American Civil War.  The house and family items were donated to the Historical Society of Dauphin County in 1941, which now operates it as a museum.  The mansion was declared a National Historic Landmark in 1975, and is located in the Harrisburg Historic District.

Warden's House Museum: The Warden's House Museum is a historic house museum in Stillwater, Minnesota, United States.  From 1853 to 1914 it was the official residence for the wardens of the Minnesota Territorial Prison, which became the Minnesota State Prison upon statehood in 1858.  The Washington County Historical Society has operated the house since 1941, making it the second-oldest house museum in Minnesota.  It was listed on the National Register of Historic Places in 1974 as the Minnesota Territorial/State Prison Warden's House for having state-level significance in the themes of architecture and social history.  It was nominated for being the only surviving structure of the prison's Minnesota Territory period and the chief remnant of its statehood years.

Thomas Dodge Homestead: Thomas Dodge Homestead is a historic home located at Port Washington in Nassau County, New York.  It is a settlement era farmhouse dated to 1721 with additions completed about 1750 and in 1903.  It is a 1 ⁄ -story, L-shaped heavy timber-frame building sheathed with natural cedar wood shingles.  The main block has a saltbox shape and there is a nearly square, 1 ⁄ -story gable-roofed wing.  Also on the property are a contributing barn (1880), privy (1886), chicken coop, and shed.  It is operated as a historic house museum by the Cow Neck Peninsula Historical Society, which has its headquarters in the Sands-Willets Homestead, another historic house museum.

Glensheen Historic Estate: Glensheen, the Historic Congdon Estate is a 27,000 square foot mansion in Duluth, Minnesota, United States, operated by the University of Minnesota Duluth as a historic house museum.  Glensheen sits on 12 acres of waterfront property on Lake Superior, has 39 rooms and is built in the Jacobean architectural tradition, inspired by the Beaux-Arts styles of the era.  The mansion was constructed as the family home of Chester Adgate Congdon.  The building was designed by Minnesota architect Clarence H. Johnston Sr., with interiors designed by William A. French Co. and the formal terraced garden and English style landscape designed by the Charles Wellford Leavitt firm out of New York.  Construction began in 1905 and completed in 1908.  The home is a crowning example of design and craftmanship of the Midwest in the early 20th century.

Jemison–Van de Graaff Mansion: The Jemison–Van de Graaff Mansion, also known as the Jemison–Van de Graaf–Burchfield House, is a historic house in Tuscaloosa, Alabama, United States.  The structure remained a private residence until 1955, when it served first as a library, then publishing house offices, and lastly as a historic house museum.  The mansion was added to National Register of Historic Places on April 19, 1972, due to its architectural significance.

Colbert House (Ilwaco, Washington): The Colbert House is a historic house museum owned by Washington State Parks and located in Ilwaco, Washington, at the corner of Spruce and Quaker streets.  The house was originally built in 1872 and was moved to its current site in 1883.  The house was owned by a fishing family and was restored in 1994 to a late 19th-century appearance with Colbert family furnishings and decorative items.  Following its restoration, the house was operated by Cape Disappointment State Park as a historic house museum that was open by appointment only.  In 2009, the Long Beach Area Parks Management Plan deemed the operation of the building as a house museum to be "not feasible at this time" and that "State Parks will preserve the building until such time as a feasible and sustainable use becomes apparent."

John A. North House: The John A. North House is a historic house museum and archives located in Lewisburg, Greenbrier County, West Virginia.  Currently, the North House is Greenbrier County's only historic house museum.  Since 1976, The Greenbrier Historical Society has operated within the North House, and in 1992 the North House was officially purchased by the Greenbrier Historical Society.  In 1992, the home officially became known as " North House Museum, Greenbrier Historical Society."

Chester Adgate Congdon: Chester Adgate Congdon (June 12, 1853 – November 21, 1916), lawyer and capitalist, was born in Rochester, New York, on June 12, 1853, his parents being Sylvester Laurentius and Laura Jane (Adgate) Congdon.  The Congdon name is indelibly linked with the Glensheen Historic Estate in Duluth, Minnesota.

Salisbury Mansion and Store: The Salisbury Mansion and Store is an historic house museum at 40 Highland Street in Worcester, Massachusetts.  The house was originally built on Lincoln Square in 1772 by Stephen Salisbury I with an attached storehouse from which he sold imported goods under the name "S. & S. Salisbury".  He and his brother Samuel had originally been in business together selling hardware goods in Boston, and Stephen moved to Worcester to expand the operation.  In 1820 the store was closed down, and the space was converted for residential use by the family, which occupied it until 1851.  Thereafter it served as a girls' school, tenant house, and then a gentleman's social club until 1929, when the building was threatened with demolition by the then occupants, the Worcester Lincoln Square Boys Club, who wanted to build more modern premises.  It was saved by local efforts and moved to its current location on the former Salisbury estate near the museum and next to Salisbury House.  It was donated to the American Antiquarian Society, which promptly gave it to the Worcester Art Museum, both of which were founded by Stephen Salisbury III.  The museum undertook to restore the much-altered building to its condition as of 1830, and opened it for group tours as a historic house museum.

Supporting paragraphs: Chester Adgate Congdon Glensheen Historic Estate
Answer: 27,000