According to the United States Census Bureau, the CDP has a total area of 2.9 square miles (7.5 km²), all land.
There were 10,187 households out of which 31.4% had children under the age of 18 living with them, 62.9% were married couples living together, 10.4% had a female householder with no husband present, and 23.1% were non-families. 19.9% of all households were made up of individuals and 11.3% had someone living alone who was 65 years of age or older. The average household size was 2.87 and the average family size was 3.30.
In the CDP the population was spread out with 22.0% under the age of 18, 7.1% from 18 to 24, 29.6% from 25 to 44, 22.7% from 45 to 64, and 18.6% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 89.9 males. For every 100 females age 18 and over, there were 86.3 males.
The median income for a household in the CDP was $60,998, and the median income for a family was $69,420. Males had a median income of $50,805 versus $35,207 for females. The per capita income for the CDP was $24,149. About 3.7% of families and 5.0% of the population were below the poverty line, including 4.8% of those under age 18 and 7.7% of those age 65 or over.
Franklin Square was the home of the Franklin National Bank, once the nation's 20th largest bank. Under the leadership of Arthur T. Roth, the Franklin National Bank introduced many banking innovations, such as
On 8 October 1974, the Franklin National Bank was declared insolvent due to mismanagement and fraud, involving losses in foreign currency speculation and poor loan policies. This caused massive losses for its stockholders, resulted in jail and disgrace for its management; Italian financier and CEO Michele Sindona was poisoned in his cell in 1986 while serving a life-sentence for his part in this affair. It was at the time the largest bank failure in the history of the country, and forced US banking policymakers to reexamine and reassess regulation of international banking.