New Jersey's 39th legislative district is one of 40 in the state, including portions of Bergen County. Included are the Bergen County municipalities of Allendale, Alpine, Cresskill, Closter, Demarest, Dumont, Emerson, Harrington Park, Haworth, Hillsdale, Ho-Ho-Kus, Mahwah, Midland Park, Montvale, Northvale, Norwood, Oakland, Old Tappan, Park Ridge, Ramsey, River Vale, Rockleigh, Saddle River, Upper Saddle River, Waldwick, Washington Township, Westwood, and Woodcliff Lake.
As of the 2020 United States census, the district had a population of 217,994, of whom 172,439 (79.1%) were of voting age. The racial makeup of the district was 162,440 (74.5%) White, 4,051 (1.9%) African American, 645 (0.3%) Native American, 26,509 (12.2%) Asian, 31 (0.0%) Pacific Islander, 7,565 (3.5%) from some other race, and 16,753 (7.7%) from two or more races. Hispanic or Latino people of any race were 22,937 (10.5%) of the population.
The district had 191,537 registered voters , of whom 76,170 (39.9%) were registered as unaffiliated, 56,888 (29.8%) were registered as Democrats, 57,082 (29.9%) were registered as Republicans, and 1,387 (0.7%) were registered to other parties.
The district, which covers most of Northern Bergen County, has the smallest African-American population of any district in the state and ranks 31st in the number of Hispanic residents, while it has the ninth-highest percentage of Asian residents. At 0.3% it has the lowest percentage of children receiving Temporary Assistance for Needy Families aid, just over 5% of the state average. The district ranked second-highest in both equalized property value and personal income on a per capita basis.
The legislative district is located within New Jersey's 5th congressional district and New Jersey's 9th congressional district.
Throughout most of the district's history since 1973, the year the 40-district legislative map was created in New Jersey, the 39th district has encompassed the small affluent boroughs and townships in northeast Bergen County. In the redistricting of 1981 and 1991, only a few municipalities were added and removed to get the district's population close to one-fortieth of the state's population as required under the Reynolds v. Sims ruling.
Changes to the district made as part of the New Jersey Legislative apportionment in 2001 removed Englewood Cliffs and Tenafly (to the 37th legislative district added Oradell (from the 38th legislative district) and Waldwick and Washington Township (from the 40th legislative district).
With Democrat Brendan Byrne at the top of the ticket winning the race for Governor of New Jersey, Frank Herbert won the 1977 race for Senate in the 39th district, standing together with his running mates in support of the establishment of a state income tax to defeat Republican John Markert.
In the 1979 election, Gerald Cardinale and Markert defeated incumbent Democrat Greta Kiernan, who had herself defeated Markert two years earlier.
Cardinale knocked off the incumbent State Senator Frank Herbert in 1981 and Herbert fell short again running against Cardinale in 1983, losing by about 1,000 votes.
Citing recent hip replacement surgery as a factor, John E. Rooney announced in March 2009 that he would not seek another term of office and would retire after 26 years in the legislature. He endorsed Bob Schroeder, a Washington Township councilmember, who won election to succeed him. After Charlotte Vandervalk decided not to run for re-election in 2011, Holly Schepisi ran in her place and won together with the other Republican incumbents.
Changes to the district made as part of the New Jersey Legislative apportionment in 2011 removed several Bergen County municipalities and added portions of Passaic County and northwest Bergen County.
Gerald Cardinale died in office on February 20, 2021, after 12 terms in office. Holly Schepisi won a Republican Party special convention over Robert Auth to fill the vacant senate seat and was sworn in on March 25, 2021. Upper Saddle River council member DeAnne DeFuccio edged out John V. Azzariti and was chosen by Republicans to fill the Assembly seat vacated by Schepisi; she took office on April 9, 2021.
On February 2, 2023, DeFuccio announced that she would not seek re-election to the Assembly, despite previously announcing her candidacy, and John Azzariti was chosen to fill DeFuccio's slot in the 2023 New Jersey General Assembly election.