Riverdale was incorporated as a borough by an Act of the New Jersey Legislature on March 12, 1923, from portions of Pequannock Township, subject to the results of a referendum passed on April 17, 1923.
As of the census of 2000, there were 2,498 people, 919 households, and 671 families residing in the borough. The population density was 1,215.2 people per square mile (468.2/km²). There were 940 housing units at an average density of 457.3/sq mi (176.2/km²). The racial makeup of the borough was 93.39% White, 1.08% African American, 0.04% Native American, 2.72% Asian, 1.60% from other races, and 1.16% from two or more races. Hispanic or Latino of any race were 4.40% of the population.
Riverdale has a very substantial Italian population, with 25.1% of residents reporting that they were of Italian ancestry in the 200 census.
There were 919 households out of which 32.1% had children under the age of 18 living with them, 60.2% were married couples living together, 10.0% had a female householder with no husband present, and 26.9% were non-families. 21.1% of all households were made up of individuals and 7.4% had someone living alone who was 65 years of age or older. The average household size was 2.68 and the average family size was 3.14.
In the borough the population was spread out with 23.5% under the age of 18, 7.4% from 18 to 24, 33.5% from 25 to 44, 23.6% from 45 to 64, and 12.1% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 94.1 males. For every 100 females age 18 and over, there were 90.7 males.
The median income for a household in the borough was $71,083, and the median income for a family was $79,557. Males had a median income of $50,457 versus $41,420 for females. The per capita income for the borough was $31,187. About 3.0% of families and 5.3% of the population were below the poverty line, including 6.9% of those under age 18 and 3.7% of those age 65 or over.