Allenstown is located in Merrimack county New hampshire with a geographic area of square miles. The total population in Allenstown is 4,428 with 51.0% male and 49.0% female. Children under age 5 represent 5.1% of the population, under age 18 equal 21.3% of the population and over age 65 is 16.2% of the population. The median household income is $57,601, per capita income is $27,118. There are a total of 1,781 housing units with 77.3% owner occupied. Education includes 34.3% of residents that are high school graduates and 17.3% with a bachelor's degree or higher. The average temperature in Allenstown in the summer is 68 degrees, and in the winter 23 degrees.