[3] Deer Creek and Bull Creek have their headwaters in the southeastern section of the township, whence they flow south to the Allegheny River in Allegheny County.

[4] As of the 2000 census,[6] there were 5,586 people, 2,045 households, and 1,615 families residing in the township.

There were 2,105 housing units at an average density of 91.7 per square mile (35.4/km2).

18.1% of all households were made up of individuals, and 8.0% had someone living alone who was 65 years of age or older.

Middlesex Township is within the Mars Area School District.