As of the census of 2000, there were 17,334 people, 6,993 households, and 4,643 families residing in the town. The population density was 515.6/km² (1,335.4/mi²). There were 7,603 housing units at an average density of 226.2/km² (585.7/mi²). The racial makeup of the town was 89.12% White, 4.72% African American, 0.36% Native American, 2.18% Asian, 0.11% Pacific Islander, 1.07% from other races, and 2.43% from two or more races. Hispanic or Latino of any race were 2.93% of the population.
There were 6,993 households out of which 32.9% had children under the age of 18 living with them, 53.9% were married couples living together, 9.8% had a female householder with no husband present, and 33.6% were non-families. 28.7% of all households were made up of individuals and 10.9% had someone living alone who was 65 years of age or older. The average household size was 2.43 and the average family size was 3.01.
In the town the population was spread out with 25.0% under the age of 18, 6.6% from 18 to 24, 30.9% from 25 to 44, 22.6% from 45 to 64, and 14.9% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 94.8 males. For every 100 females age 18 and over, there were 89.7 males.
The median income for a household in the town was $51,075, and the median income for a family was $57,322. Males had a median income of $41,778 versus $27,229 for females. The per capita income for the town was $25,857. About 3.7% of families and 5.0% of the population were below the poverty line, including 6.2% of those under age 18 and 4.7% of those age 65 or over.
Middletown is home to St Columba's Cricket Club, which hosts an annual cricket tournament for teams throughout the New England area.