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Abandoned factory along the Allegheny River
|Motto(s): Proud City of Proud People|
Location of Arnold in Westmoreland County, Pennsylvania.
|• Mayor||Karen Peconi-Biriccochi (D)|
|• Total||0.82 sq mi (2.13 km2)|
|• Land||0.73 sq mi (1.90 km2)|
|• Water||0.09 sq mi (0.23 km2)|
|• Estimate (2016)||4,939|
|• Density||6,747.27/sq mi (2,605.00/km2)|
|Time zone||UTC-5 (Eastern (EST))|
|• Summer (DST)||UTC-4 (EDT)|
Present-day Westmoreland County was part of the hunting reserves of the Iroquois Indians. White colonists began to penetrate the area in the 1750s, and circa 1781 Robert McCrea purchased the land on which Arnold is situated. William Jack acquired the property and later passed it on to Wilson Jack. The area around Arnold was first settled in 1852 by Major Andrew Arnold, who grew up in Kittanning.
Arnold was part of New Kensington until it was separately incorporated as a borough in January 1896, and as a third-class city in 1939. Arnold is governed under Pennsylvania's third-class city code, with a mayor and four council members elected at-large. Past mayors of Arnold have been M. Frank Horne (1939-1960), Alfred Colaianni (1960-1963), Willie DeMao (1963-2004), John Campbell (2004-2012), and Larry Milito (2012-2016).
The current mayor, Karen Peconi-Biriccochi, a Democrat, took office in 2016. While in office due to protests in reaction to the killing of an unarmed African-American teen Antwon Rose by a white police officer in East Pittsburgh, Mayor Peconi urged law enforcement to "bring the hoses" against the protesters. She later apologized, however, faces calls for her resignation. 
Arnold is located on the eastern shore of the Allegheny River, northeast of Pittsburgh. According to the United States Census Bureau, the city has a total area of 0.8 square miles (2.1 km2), of which 0.7 square miles (1.8 km2) is land and 0.1 square miles (0.26 km2) (6.41%) is water.
Surrounding and adjacent neighborhoods
As of the census of 2000, there were 5,667 people, 2,589 households, and 1,439 families residing in the city. The population density was 7,706.6 people per square mile (2,956.8/km²). There were 2,976 housing units at an average density of 4,047.1 per square mile (1,552.8/km²). The racial makeup of the city was 84.84% White, 12.76% African American, 0.18% Native American, 0.14% Asian, 0.02% Pacific Islander, 0.26% from other races, and 1.80% from two or more races. Hispanic or Latino of any race were 1.13% of the population.
There were 2,589 households of which 23.6% had children under the age of 18 living with them, 37.5% were married couples living together, 14.4% had a female householder with no husband present, and 44.4% were non-families. 39.9% of all households were made up of individuals and 20.7% had someone living alone who was 65 years of age or older. The average household size was 2.15 and the average family size was 2.90.
In the city, the population was spread out with 21.6% under the age of 18, 6.9% from 18 to 24, 28.7% from 25 to 44, 20.2% from 45 to 64, and 22.6% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 86.5 males. For every 100 females age 18 and over, there were 82.9 males.
The median income for a household in the city was $26,190, and the median income for a family was $32,569. Males had a median income of $31,164 versus $23,953 for females. The per capita income for the city was $16,631. About 14.0% of families and 17.7% of the population were below the poverty line, including 30.8% of those under age 18 and 10.3% of those age 65 or over.
Notable landmarks in Arnold have included:
- Arnold Station, established in 1867, which was Arnold’s railroad stop. It was so named because the land on which it was built was given by the Arnold Family.
- The Chambers Glass Company, which opened in 1891, was at the time the first, best equipped, and most efficient glass plant in the country.
- George Moore Home, which was built with 17 rooms, but has since been demolished.
- The Morris Davis home stands across from where the George Moore home stood. Morris Davis built it very precisely, rejecting many loads of lumber if they had knotholes or any defects. It was one of the very first homes in the area that had electricity.
- The Hartley Howard Home was another home of that time, which still stands today, serving as apartments.
- Eiler Hall was a fashionable site for parties, dances, banquets and public shows. It is now a parking lot for city employees of the Municipal Building.
- The Edna Hotel was named after George Moore‘s daughter Edna in the late 1800s. It was the meeting place for all of Arnold at the turn of the 20th century. The building was destroyed by a massive fire in the late 1990s and is now a vacant grass lot.
- The John Fedan Store began as a rental for other merchants. When that did not follow through, Fedan started his own business with a small hardware store and later added a furniture and appliance store.
- The Arnold Drug Store opened in 1898 and was also the post office location at the time.
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Arnold is served by the New Kensington–Arnold School District, which includes four schools in New Kensington and Arnold: Valley Jr/Sr High School, three elementary schools. Roy A. Hunt Elementary (Arnold), H.D. Berkey School (Arnold), and Martin Elementary School (New Kensington).
The current Roy A. Hunt Elementary once served as Arnold's high school prior to the merger of the two districts. After the merge was completed it was used as Valley Middle School until the restructuring of the school district at the end of 2012, and now stands as an elementary school holding grades 3-6
- Clara Chiano (1921–2000), American Girls Professional Baseball League player
- Johnny Costa (1922–1996), jazz pianist
- Fannie Sellins (1872–1919), labor activist
- "2016 U.S. Gazetteer Files". United States Census Bureau. Retrieved Aug 14, 2017.
- "Population and Housing Unit Estimates". Retrieved June 9, 2017.
- "Census 1990" (PDF). Census.gov. Retrieved 2015-09-18.
- "Incorporated Places and Minor Civil Divisions Datasets: Subcounty Resident Population Estimates: April 1, 2010 to July 1, 2012". Population Estimates. U.S. Census Bureau. Archived from the original on 17 June 2013. Retrieved 11 December 2013.
- "Profile of General Demographic Characteristics: 2000 - Geographic area: Arnold city, Pennsylvania" (PDF). Censtats.census.gov. Retrieved 2015-09-18.
- The Woman's Club of New Kensington. Lore of Yore. New Kensington, Pennsylvania: Buhl Brothers Printing,1986.