The district had 151,184 registered voters as of February 28, 2019[update], of whom 65,125 (43.1%) were registered as unaffiliated, 52,524 (34.7%) were registered as Democrats, 32,368 (21.4%) were registered as Republicans, and 1,167 (0.8%) were registered to other parties.
Since the creation of the 40-district legislative map in 1973, the 38th District has always included Paramus, though early in the lifetime of the 40-district map, Hackensack was also within the district. In the 1973 version of the map, and in the decade following the 1981 redistricting, Paramus and Hackensack anchored the 38th District with numerous nearby municipalities in central Bergen County compromising the remainder of the district. In the 1991 redistricting, the 38th became more of a crescent shape stretching from Cliffside Park and Palisades Park, northwest to Elmwood Park, then north and east to Paramus and Oradell. This shape was slightly modified in 2001 when that year's redistricting extended the 38th to the Hudson River picking up Fort Lee and Edgewater. The crescent shape of the district was removed in the
2011 redistricting when it changed to a T-shaped district extending out of Bergen County for the first time.
In October 2015, Anthony Cappola left the race for an Assembly seat in the 38th District and resigned from office as a member of the River Edge Borough Council, following disclosures that he had written and published a 2003 book titled Outrageous that was described as "full of racial slurs, rants and stereotypes". The Bergen County Republican Organization filed suit in Passaic County, seeking to replace Cappola's spot on the ballot with Fernando Alonso and offering to cover the $100,000 cost of reprinting ballots. Bergen County Clerk John Hogan argued that absentee ballots had already been printed and distributed, with nearly ballots already completed and submitted to the Clerk's Office. The Republicans unexpectedly dropped the effort to have the candidate replaced on October 13 and Cappola later announced his intention to continue in the race. Ultimately Cappola and his running mate Mark DiPisa were defeated by Democratic incumbents Tim Eustace and Joseph Lagana.
All three seats became vacant in 2018. Robert M. Gordon resigned his Senate seat on April 4, 2018 to accept an appointment to the New Jersey Board of Public Utilities. Democratic committee members in Bergen and Passaic Counties unanimously selected Assemblyman Lagana over Assemblyman Eustace (after the latter withdrew to back Lagana) to replace Gordon in the Senate on April 11; he took his Senate seat on April 12. The following day on April 13, Eustace resigned his seat to become Deputy Director of the North Jersey District Water Supply Commission. Committee members selected Fair Lawn Mayor Lisa Swain and Congressional aide and former Bergenfield Council President Chris Tully as the replacements in the Assembly; they were sworn in on May 24.
^Ensslin, John C.; and Pugliese, Nicholas. "Outrageous author quits council seat in River Edge", The Record (Bergen County), October 2, 2015. Accessed October 7, 2015. "Embattled Republican Anthony Cappola resigned as a River Edge councilman Friday, one day after stepping down as a GOP Assembly candidate following disclosures that he had authored a book full of racial slurs, rants and stereotypes."
^Ensslin, John C. "Judge halts ballot printing until court rules on Bergen GOP replacing Assembly candidate", The Record (Bergen County), October 6, 2015. Accessed October 7, 2015. " A judge Tuesday ordered Bergen County election officials to stop processing vote-by-mail ballots in the hotly-contested 38th Legislative District until the court can rule on whether Republicans should be able to replace an Assembly candidate who has quit the race.Bergen County Clerk John Hogan said his office was instructed by a clerk for a Superior Court judge in Passaic County around 2 p.m. to halt work in the district where former GOP candidate Anthony Cappola had dropped out last week amid furor over a book he had written."