[20] Located on the northern end of the Somerset Hills,[21][22][23][24][25][26] Mendham Township is situated in the Raritan Valley region[27] within the New York Metropolitan area.

[30][31] The long-established hamlets of Brookside and Ralston are located within Mendham, and both are listed on the National Register of Historic Places.

[36] Based on data from the ACS for 2014–2018, Mendham Township ranked fifth in the state with a median household income of $185,882.

[40] Natural resources of water, forests and minerals drew settlers to the area.

On the eastern side of Mendham Township, brooks that formed the upper reaches of the Whippany River attracted settlers to the valley called Water Street or Waterville, later known as Brookside.

Following the Civil War, wealthy industrialists and financiers established country homes in the Morristown area and Bernardsville's "Mountain Colony", including in the Mendhams.

[1][2] Unincorporated communities, localities and place names located partially or completely within the township include Brookside, Colemans Hollow, Days Mills, Pleasant Valley, Ralston and Washington Corner.

[43] The long-established hamlets of Brookside and Ralston are located within the township and both are listed among the National Register of Historic Places.

[45][46][47] The 2010 United States census counted 5,869 people, 1,952 households, and 1,659 families in the township.

[59] Mendham Township is one of the highest-income small municipalities in the United States and was ranked 7th in New Jersey in per capita income as of the 2010 Census.

[60] As of the 2000 United States census[14] there were 5,400 people, 1,788 households, and 1,539 families residing in the township.

In 2000, the township's median household income ranked forth in the state and second highest in Morris County behind Mountain Lakes.

[61] In addition to the several parks in the township, there are miles of hiking trails, including the Patriots' Path, created by the county.

[75][76] Former township committeeman Brian Phelan was inducted into the New Jersey State Elected Officials Hall of Fame in 2011.

[79][80][81] For the 119th United States Congress, New Jersey's 7th congressional district is represented by Thomas Kean Jr. (R, Westfield).

[82] For the 119th United States Congress, New Jersey's 11th congressional district is represented by Mikie Sherrill (D, Montclair).

[84] For the 2024-2025 session, the 25th legislative district of the New Jersey Legislature is represented in the State Senate by Anthony M. Bucco (R, Boonton Township) and in the General Assembly by Christian Barranco (R, Jefferson Township) and Aura K. Dunn (R, Mendham Borough).

[86] Actual day-to-day operation of departments is supervised by County Administrator Deena Leary.

[128] The district's board of education is comprised nine members who are elected directly by voters to serve three-year terms of office on a staggered basis.

NJ Transit offered service on the MCM4 and MCM5 routes until 2010, when subsidies to the local provider were eliminated as part of budget cuts.