The average household size was 2.73 and the average family size was 3.22. For every 100 females ages 18 and old there were 91.8 males.
In the borough, the population was spread out with 22.5% under the age of 18, 8.1% from 18 to 24, 26.1% from 25 to 44, 29.5% from 45 to 64, and 13.8% who were 65 years of age or older. The Census Bureau's 2006-2010 American Community Survey showed that (in 2010 inflation-adjusted dollars) median household income was ,338 (with a margin of error of /- ,790) and the median family income was ,817 ( /- ,746).
In almost all cases, it can review and approve the actions of other Middlesex Borough, committees and agencies.
The Mayor and Borough Council conducts all of its business during monthly meetings open to the public.
There were already a few schools set up before Middlesex became a borough in 1913.
The Harris Lane School was a one-room schoolhouse and it was the oldest school in Middlesex County, at one time, dating back to its construction in the 1790s.
The original Pierce School was known as the East Bound Brook School House and The Parker House was also used for education until it was converted into a two-family house.
There were 4,984 households out of which 32.0% had children under the age of 18 living with them, 56.0% were married couples living together, 11.8% had a female householder with no husband present, and 27.1% were non-families.
22.2% of all households were made up of individuals, and 10.8% had someone living alone who was 65 years of age or older.