Willow Avenue and Poplar Street
|Named for: Local farm named "Castle Shanahan"|
|Elevation||1,040 ft (317 m)|
|Area||1.6 sq mi (4.1 km2)|
|- land||1.6 sq mi (4.1 km2)|
|- water||0.0 sq mi (0 km2), 0%|
|Density||5,197.5 / sq mi (2,006.8 / km2)|
|Incorporated||December 20, 1919|
|Mayor||Donald J. Baumgarten (D)|
|- summer (DST)||EDT (UTC-4)|
|School District||Keystone Oaks|
Surrounding communities 
The first families settled Castle Shannon in 1786 in pursuit of farmland and timber. The most prominent farm was owned by David Strawbridge, who named it Castle Shanahan. Over time, the farm would lend its name to the area, as "Shanahan" would evolve into "Shannon".
In 1872, the Pittsburgh and Castle Shannon Railroad line was completed, providing a direct link from Pittsburgh to the then-village of Castle Shannon. Development was stimulated by two years of free transportation and lumber transport given to anybody building a home. In 1877, a second railroad was built from Finleyville through Castle Shannon to the West End neighborhood of Pittsburgh. In 1909, the right of way through the valley containing Castle Shannon was purchased by the Pittsburgh Railroad. This helped lead to Castle Shannon becoming a center for coal mining, with eight mines in operation in 1904. The Pittsburgh and West Virginia Railroad, still active today, came shortly afterward.
The First National Bank in Castle Shannon was the site of a much publicized bank robbery in 1917. $18,500 was taken in the robbery, of which $10,500 was immediately recovered from one man shot during the escape. The full sum was never recovered.
As of the census of 2000, there were 8,556 people, 3,859 households, and 2,288 families residing in the borough. The population density was 5,259.8 people per square mile (2,026.7/km²). There were 4,037 housing units at an average density of 2,481.8 per square mile (956.3/km²). The racial makeup of the borough was 96.91% White, 1.34% African American, 0.06% Native American, 0.78% Asian, 0.01% Pacific Islander, 0.39% from other races, and 0.50% from two or more races. Hispanic or Latino of any race were 0.98% of the population.
There were 3,859 households out of which 23.2% had children under age 18 living with them, 45.3% were married couples living together, 10.7% had a female householder with no husband present, and 40.7% were non-families. 35.1% of all households were made up of individuals and 12.5% had someone living alone who was 65-years-old, or older. The average household size was 2.20 persons and the average family size was 2.88 persons.
In the borough the population was spread out with 19.7% under age 18, 7.3% from 18- to 24-years-old, 32.9% from 25- to 44-years-old, 21.4% from 45- to 64-years-old, and 18.7% who were 65-years-old, or older. The median age was 39-years-old. For every 100 females there were 90.0 males. For every 100 females age 18 and over, there were 85.5 males.
The median income for a household in the borough was $38,040; and, the median income for a family was $48,586. Males had a median income of $33,013, versus $27,907 for females. The per capita income for the borough was $20,518. About 5.0% of families and 7.7% of the population were below the poverty line, including 9.4% of those under age 18 and 7.8% of those age 65-years-old, or over.
Castle Shannon’s school system, Keystone Oaks School District, is a "jointure"[clarification needed] with the boroughs of Dormont and Green Tree, comprising Dormont Elementary School, Keystone Oaks Middle School and Keystone Oaks High School. Oddly enough, none of the three communities which make up the Keystone Oaks School District share a common border, and the high school/middle school campus is located outside the district, being situated in the municipality of Mount Lebanon. Also, a small part of Castle Shannon is actually part of the Bethel Park School District. Located within Castle Shannon is Saint Anne School, a Catholic private elementary school.
Notable people 
- Lee Hartman, animator
- Dennis Miller, comedian, grew up in Castle Shannon, and attended St. Anne Elementary School and Keystone Oaks High School
- W. Scott MacDonald, Commanding Officer, 101st Airborne Division (AASLT) Band, attended Keystone Oaks High School
- Paul J. Wilhelm, former president of U.S. Steel, attended St. Anne School, class of 1956
- "Race, Hispanic or Latino, Age, and Housing Occupancy: 2010 Census Redistricting Data (Public Law 94-171) Summary File (QT-PL), Castle Shannon borough, Pennsylvania". U.S. Census Bureau, American FactFinder 2. Retrieved September 16, 2011.
- "US Board on Geographic Names". United States Geological Survey. 2007-10-25. Retrieved 2008-01-31.
- Allegheny County Municipalities Pittsburgh Post-Gazette. 2004-08-08. Retrieved on 2008-06-08.
- "American FactFinder". United States Census Bureau. Retrieved 2008-01-31.
- Wolfe, Jennifer (2012-12-30). "Obituary: Leland 'Lee' Hartman / Pittsburgh animator who once worked at Disney Feb. 27 1930 - Dec. 24, 2012". Pittsburgh Post-Gazette. Retrieved 2013-01-06.
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