According to the United States Census Bureau, the township has a total area of, of which, of it is land and of it is water. It is drained by the Lehigh River, via the Catasauqua Creek which separates it from Lehigh County. Its villages include Howertown, Kreidersville, Seemsville and Weaversville Route 329 crosses Allen Township east-to-west on its path between the boroughs of Bath and Northampton. Other local roads of note include Bullshead Road, Cherryville Road, Howertown Road/Weaversville Road, Indian Trail Road, Kreidersville Road, Old Carriage Road, Seemsville Road, and Willowbrook Road.
As of the census of 2000, there were 2,630 people, 1,001 households, and 805 families residing in the township. The population density was 237.1 people per square mile. There were 1,030 housing units at an average density of 92.9/sq mi. The racial makeup of the township was 98.67% White, 0.19% African American, 0.08% Native American, 0.08% Asian, 0.04% Pacific Islander, 0.42% from other races, and 0.53% from two or more races. Hispanic or Latino of any race were 1.10% of the population. There were 1,001 households, out of which 31.2% had children under the age of 18 living with them, 70.7% were married couplesliving together, 5.6% had a female householder with no husband present, and 19.5% were non-families. 14.7% of all households were made up of individuals, and 5.7% had someone living alone who was 65 years of age or older. The average household size was 2.63 and the average family size was 2.91. In the township the population was spread out, with 21.7% under the age of 18, 6.3% from 18 to 24, 27.5% from 25 to 44, 31.2% from 45 to 64, and 13.3% who were 65 years of age or older. The median age was 42 years. For every 100 females, there were 97.4 males. For every 100 females age 18 and over, there were 98.3 males. The median income for a household in the township was $54,464, and the median income for a family was $59,702. Males had a median income of $41,219 versus $27,930 for females. The per capita income for the township was $23,859. About 1.1% of families and 1.7% of the population were below the poverty line, including 1.6% of those under age 18 and 1.4% of those age 65 or over.
