Holmdel Township is a township located in Monmouth County, New Jersey. As of the 2000 census, the township had a total population of 15,781.
In 1964, Arno Penzias and Robert Wilson discovered the cosmic microwave background radiation while working in this town.
According to the United States Census Bureau, the township has a total area of 46.9 km² (18.1 mi²). 46.5 km² (18.0 mi²) of it is land and 0.3 km² (0.1 mi²) of it is water. The total area is 0.66% water.
As of the census of 2000, there are 15,781 people, 4,947 households, and 4,328 families residing in the township. The population density is 339.1/km² (878.4/mi²). There are 5,137 housing units at an average density of 110.4/km² (285.9/mi²). The racial makeup of the township is 80.20% White, 0.65% African American, 0.03% Native American, 17.45% Asian, 0.01% Pacific Islander, 0.52% from other races, and 1.15% from two or more races. 2.45% of the population are Hispanic or Latino of any race.
There are 4,947 households out of which 47.1% have children under the age of 18 living with them, 79.1% are married couples living together, 6.7% have a female householder with no husband present, and 12.5% are non-families. 11.1% of all households are made up of individuals and 4.3% have someone living alone who is 65 years of age or older. The average household size is 3.09 and the average family size is 3.35.
In the township the population is spread out with 28.5% under the age of 18, 5.2% from 18 to 24, 24.8% from 25 to 44, 29.2% from 45 to 64, and 12.2% who are 65 years of age or older. The median age is 41 years. For every 100 females there are 91.9 males. For every 100 females age 18 and over, there are 86.6 males.
The median income for a household in the township is $112,879, and the median income for a family is $122,785. Males have a median income of $94,825 versus $54,625 for females. The per capita income for the township is $47,898. 3.4% of the population and 2.7% of families are below the poverty line. Out of the total people living in poverty, 4.0% are under the age of 18 and 6.7% are 65 or older.