Northfield is located at 42°06?07?N 87°46?30?W / 42.101927°N 87.775079°W / 42.101927; -87.775079. According to the United States Census Bureau, the village has a total area of 3.0 square miles (7.7 km²), all of it land.
As of the census of 2000, there were 5,389 people, 2,155 households, and 1,532 families residing in the village. The population density was 1,822.4 people per square mile (702.9/km²). There were 2,241 housing units at an average density of 757.9 per square mile (292.3/km²). The racial makeup of the village was 92.48% White, 0.52% African American, 0.04% Native American, 5.57% Asian, 0.43% from other races, and 0.96% from two or more races. Hispanic or Latino of any race were 1.67% of the population.