Allendale is a village in Wabash Precinct, Wabash County, Illinois. The population was 475 at the 2010 census.
Allendale is located 4 miles (6.4 km) northeast of Patton and 1.75 miles (2.82 km) east-northeast of Adams Corner at 38°31′43″N 87°42′35″W / 38.52861°N 87.70972°W / 38.52861; -87.70972 (38.528524, -87.709811). According to the 2010 census, Allendale has a total area of 0.31 square miles (0.80 km), all land.
As of the census of 2000, there were 528 people, 192 households, and 142 families residing in the village. The population density was 1,755.5 people per square mile (679.5/km²). There were 205 housing units at an average density of 681.6 per square mile (263.8/km²). The racial makeup of the village was 97.92% White, 0.76% African American, 0.95% from other races, and 0.38% from two or more races. Hispanic or Latino of any race were 1.14% of the population.
There were 192 households out of which 35.4% had children under the age of 18 living with them, 60.9% were married couples living together, 10.4% had a female householder with no husband present, and 26.0% were non-families. 25.5% of all households were made up of individuals and 12.0% had someone living alone who was 65 years of age or older. The average household size was 2.65 and the average family size was 3.20.
In the village, the population was spread out with 28.4% under the age of 18, 10.2% from 18 to 24, 25.8% from 25 to 44, 23.7% from 45 to 64, and 11.9% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 98.5 males. For every 100 females age 18 and over, there were 93.8 males.
The median income for a household in the village was $31,705, and the median income for a family was $38,472. Males had a median income of $30,000 versus $16,719 for females. The per capita income for the village was $12,117. About 12.1% of families and 16.6% of the population were below the poverty line, including 26.4% of those under age 18 and 1.9% of those age 65 or over.