The area had been called "Brookland" in the 1800s and the lake that was expanded to become Lake Hopatcong had been known as "Great Pond" or "Brookland Pond". During the 1803s, the name of the community had been modified to "Brooklyn", to match the spelling of the city on New York's Long Island. Hopatcong was originally established as the Borough of Brooklyn on April 2, 1898 from portions of Byram Township. On March 22, 1901, the Borough of Hopatcong replaced Brooklyn. In 1922, residents of Byram Cove, Northwood, and other areas to the west of the original land area of the borough, voted to leave Byram Township and join Hopatcong, leaving the Borough with its current borders.
According to the United States Census Bureau, the borough has a total area of 12.3 square miles (32.0 km²), of which, 11.0 square miles (28.4 km²) of it is land and 1.4 square miles (3.6 km²) of it (11.18%) is water.
There were 5,656 households out of which 38.7% had children under the age of 18 living with them, 62.3% were married couples living together, 8.3% had a female householder with no husband present, and 25.1% were non-families. 18.6% of all households were made up of individuals and 4.2% had someone living alone who was 65 years of age or older. The average household size was 2.81 and the average family size was 3.24.
In the borough the population was spread out with 26.4% under the age of 18, 7.1% from 18 to 24, 34.8% from 25 to 44, 24.9% from 45 to 64, and 6.8% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 102.0 males. For every 100 females age 18 and over, there were 100.1 males.
The median income for a household in the borough was $65,799, and the median income for a family was $73,277. Males had a median income of $47,083 versus $34,238 for females. The per capita income for the borough was $26,698. About 2.2% of families and 3.0% of the population were below the poverty line, including 2.7% of those under age 18 and 5.8% of those age 65 or over.
The town of Hopatcong has a rich history given its relationship with New York City. It borders Lake Hopatcong, a partially man made lake that is now a source of much recreation and desirable real estate, and is the biggest lake in New Jersey. The town, just 40 miles west of New York City, began as a summer get away for the wealthy in NYC who primarily sought access to the lake. An amusement park sprung up called "Bertrand's Island" which was accessible via the lake or by car through Mount Arlington. The construction of Interstate 80, a highway that stretches from Teaneck, New Jersey all the way across the country to San Francisco, California, triggered rapid growth in New York City's suburbs and led to Hopatcong becoming a permanent residential community.
The Mayor is the chief executive officer of the Borough, helps set the agenda for Council meetings and chairs all meetings of the Council. The Mayor can vote only in the event of a tie but has the power to veto any ordinance adopted by the Council.
The Mayor has executive authority to act between Council meetings in matters affecting the Borough. The Mayor can declare a state of emergency and can act to protect the Borough and its citizens. The Mayor appoints the members of all Borough Committees and certain Borough Commissions. The Mayor's nominations for certain other Borough Boards and Commissions are subject to Council approval. The Mayor prepares the initial draft of the annual Borough budget for submission to the Council. The Mayor can issue Proclamations. The Mayor is authorized to perform marriage ceremonies. The Mayor is required to sit as a member of the Borough Planning Board. The signatures of the Mayor and Borough Clerk are necessary to create any legally binding obligation of the Borough.
The Borough Council is the legislative body of the Borough and can act in one of two formats: a) Ordinances, which have the effect of law and b) Resolutions, which state the policy or direction of the Council. Ordinances require public notice and a public hearing prior to adoption. Resolutions must be adopted in public but do not require public hearings.
The Council is charged with the adoption of the annual Borough Budget. The Mayor's nominations of certain Borough officials are also subject to Council approval. Council members are annually appointed by the Mayor to act as liaisons to various Borough departments, Boards, Commissions or Committees. The Council annually elects a member to serve in the position of Council President. In the absence of the Mayor, the Council President can assume the role and duties of the Mayor. The Council also annually elects a member to serve as its representative on the Planning Board.
The Mayor of Hopatcong Borough is Sylvia Petillo (R). Members of the Hopatcong Borough Council are Council President Estelle Klein (R), Rich Bunce (R, 2009), Marie Galate (I, 2009), Bob Modick, Michael Francis, and Madeline McManus (R, 2008).