Avon-by-the-Sea was incorporated as a borough by an Act of the New Jersey Legislature on March 23, 1900, from portions of Neptune City.
According to the United States Census Bureau, the borough has a total area of 0.6 square miles (1.4 km²), of which, 0.4 square miles (1.1 km²) of it is land and 0.1 square miles (0.3 km²) of it (21.82%) is water.
As of the 2000 census, 36.5% of Avon-by-the-Sea residents were of Irish ancestry, the third-highest percentage of any municipality in the United States, and second-highest in New Jersey, among all places with more than 1,000 residents identifying their ancestry.
There were 1,043 households out of which 18.6% had children under the age of 18 living with them, 42.8% were married couples living together, 6.4% had a female householder with no husband present, and 48.7% were non-families. 41.1% of all households were made up of individuals and 18.5% 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 3.04.
In the borough the population was spread out with 18.4% under the age of 18, 4.8% from 18 to 24, 28.7% from 25 to 44, 25.8% from 45 to 64, and 22.3% who were 65 years of age or older. The median age was 44 years. For every 100 females there were 93.4 males. For every 100 females age 18 and over, there were 87.4 males.
The median income for a household in the borough was $60,192, and the median income for a family was $80,605. Males had a median income of $53,125 versus $35,857 for females. The per capita income for the borough was $41,238. About 2.3% of families and 2.7% of the population were below the poverty line, including 3.0% of those under age 18 and 4.4% of those age 65 or over.
Members of the Avon-by-the-Sea Commission are:
For grades 9-12, public school students attend Manasquan High School, in Manasquan, as part of a sending/receiving relationship. The high school also serves students from Belmar, Brielle, Lake Como, Sea Girt, Spring Lake, Spring Lake Heights who attended Manasquan High School as part of sending/receiving relationships with their respective districts. During the 2004-2005 school year, there were seven students from Avon-by-the Sea who attended Manasquan High School. Students may also apply to academy schools in the Monmouth County Vocational School District, which include the Academy of Allied Health & Science, Biotechnology High School, High Technology High School, Marine Academy of Science and Technology and Communications High School.
Students may also attend Academy Charter High School, located in Lake Como, which serves residents of Allenhurst, Asbury Park, Avon-by-the-Sea, Belmar, Bradley Beach, Deal, Interlaken and Lake Como, and accepts students on a lottery basis.