As of the 2010 Census Bethany had a population of 5,563. The racial composition of the population was 91.6% white, 1.9% black or African American, 4.8% Asian, 0.6% other races and 1.1% from two or more races. 2.5% of the population was Hispanic or Latino of any race. As of the census of 2000, there were 5,040 people, 1,755 households, and 1,449 families residing in the town. The population density was 240.4 people per square mile (92.8/km²). There were 1,792 housing units at an average density of 85.5 per square mile (33.0/km²). The racial makeup of the town was 95.04% White, 1.83% African American, 0.30% Native American, 1.53% Asian, 0.10% Pacific Islander, 0.48% from other races, and 0.73% from two or more races. Hispanic or Latino of any race were 2.02% of the population.
There were 1,755 households out of which 40.2% had children under the age of 18 living with them, 73.8% were married couples living together, 6.6% had a female householder with no husband present, and 17.4% were non-families. 13.5% of all households were made up of individuals and 5.5% had someone living alone who was 65 years of age or older. The average household size was 2.87 and the average family size was 3.18.
In the town, the population was spread out with 27.3% under the age of 18, 4.6% from 18 to 24, 27.4% from 25 to 44, 28.4% from 45 to 64, and 12.3% who were 65 years of age or older. The median age was 41 years. For every 100 females, there were 99.5 males. For every 100 females age 18 and over, there were 95.1 males. The median income for a household in the town was $74,898, and the median income for a family was $79,493. Males had a median income of $52,037 versus $44,427 for females. The per capita income for the town was $31,403. About 1.5% of families and 2.6% of the population were below the poverty line, including 4.1% of those under age 18 and 0.6% of those age 65 or over.