McNerney was raised in Teaneck, New Jersey, attending a Catholic grammar school in neighboring Bogota. He attended Bergen Catholic High School in Oradell, New Jersey, and went to college at Bergen Community College and the University of Delaware before receiving an M.P.A. degree from Columbia University. McNerney and his family live in Ho-Ho-Kus.
He took office in January 2003 after being twice elected to the Bergen County Board of Chosen Freeholders, in 1998 and 2001, defeating Republican Henry McNamara. In succeeding Pat Schuber, McNerney became the first Democrat to hold the post of Bergen County Executive. McNerney was reelected to a second term of office as County Executive in 2006, defeating former Freeholder Todd Caliguire. He lost reelection in the 2010 election to Kathleen Donovan in a race in which the Republicans captured all three open seats on the Board of Chosen Freeholders to regain control on the board.
In his February 2008 State of the County address, McNerney called for municipalities with populations less than 10,000 in Bergen County to merge, saying "The surest way to significantly lower homeowners' property taxes is to merge small towns and reduce administrative overhead." Half of Bergen County's 70 municipalities have fewer than 10,000 residents each.
- Demetriades, Andoni. "2010 State of the County", The Torch student newspaper of Bergen Community College, p. 7. April 2010. Accessed September 19, 2011. "McNerney, who happens to be a graduate of BCC, then began his address. He spoke about his long history in the county, how he grew up in Teaneck and attended grammar school in Bogota."
- County Executive Dennis McNerney Archived December 6, 2006, at the Wayback Machine., Bergen County, New Jersey. Accessed February 16, 2011. "Dennis McNerney is a lifelong resident of Bergen County. He graduated from Bergen Catholic High School, attended Bergen Community College, the University of Delaware, and went on to receive his Masters Degree in Public Administration from Columbia University.... He currently resides in Ho-Ho-Kus with his wife Catherine and their two children."
- Jones, Richard Lezin. "THE 2002 ELECTIONS: NEW JERSEY; Supporter of Newark Arena Is Elected Essex Executive", The New York Times, November 6, 2002. Accessed February 16, 2011. "In Bergen County, Dennis McNerney, a two-term Democratic freeholder, defeated Henry P. McNamara, a veteran Republican state senator, in the race for county executive."
- James, George. "GOVERNMENT; It's County vs. Mayor", The New York Times, April 4, 2004. Accessed February 16, 2011. "Mr. McNerney took office last year and is the first Democrat to hold the post. Efforts to build a shelter eluded his Republican predecessor, William P. Schuber, who suggested building one in 1998."
- Gartland, Michael. "Donovan leads Republican sweep in Bergen", The Record (Bergen County), November 2, 2010. Accessed February 16, 2011.
- "County exec urges mergers of towns". NorthJersey.com. 2008-02-08. Archived from the original on 2008-02-14. Retrieved 2008-02-08.