Rensselaer is located southwest of the center of Jasper County at . It is bordered to the south by the unincorporated community of Collegeville, home to the now-closed Saint Joseph's College. The Iroquois River, a tributary of the Kankakee River and hence part of the Illinois River watershed, flows from east to west through the south part of the city. U.S. Route 231 and Indiana State Road 114 intersect in the downtown area. US-231 leads north to DeMotte and south to Remington, while State Road 114 leads east to U.S. Route 421 and west to Interstate 65. Via I-65, Rensselaer is north of Lafayette and south of Gary. According to the 2010 census, Rensselaer has a total area of, of which is land and is water.
At the 2010 census there were 5,859 people, 2,336 households, and 1,517 families living in the city. The population density was. There were 2,556 housing units at an average density of. The racial makup of the city was 95.4% White, 0.7% African American, 0.4% Native American, 0.4% Asian, 0.1% Pacific Islander, 1.8% from other races, and 1.3% from two or more races. Hispanic or Latino of any race were 5.4%. Of the 2,336 households 33.4% had children under the age of 18 living with them, 44.9% were married couples living together, 14.7% had a female householder with no husband present, 5.4% had a male householder with no wife present, and 35.1% were non-families. 29.5% of households were one person and 12.6% were one person aged 65 or older. The average household size was 2.42 and the average family size was 2.96. The median age was 36.6 years. 25.5% of residents were under the age of 18; 8.7% were between the ages of 18 and 24; 25.6% were from 25 to 44; 23.7% were from 45 to 64; and 16.4% were 65 or older. The gender makeup of the city was 48.0% male and 52.0% female.
2000 census
At the 2000 census there were 5,294 people, 2,158 households, and 1,404 families living in the city. The population density was 1,824.8 people per square mile. There were 2,296 housing units at an average density of 791.4 per square mile. The racial makup of the city was 97.94% White, 0.32% African American, 0.21% Native American, 0.09% Asian, 0.66% from other races, and 0.77% from two or more races. Hispanic or Latino of any race were 2.53%. Of the 2,158 households 31.2% had children under the age of 18 living with them, 50.1% were married couples living together, 10.8% had a female householder with no husband present, and 34.9% were non-families. 31.1% of households were one person and 15.6% were one person aged 65 or older. The average household size was 2.37 and the average family size was 2.98. The age distribution was 25.3% under the age of 18, 9.4% from 18 to 24, 26.9% from 25 to 44, 20.0% from 45 to 64, and 18.5% 65 or older. The median age was 36 years. For every 100 females, there were 89.0 males. For every 100 females age 18 and over, there were 83.4 males. The median household income was $34,821 and the median family income was $43,313. Males had a median income of $33,971 versus $24,016 for females. The per capita income for the city was $20,872. About 6.6% of families and 10.0% of the population were below the poverty line, including 11.8% of those under age 18 and 8.0% of those age 65 or over.
Climate
Humid continental climate is a climatic region typified by large seasonal temperature differences, with warm to hot summers and cold winters. Precipitation is relatively well distributed year-round in many areas with this climate, while others may see a marked reduction in wintry precipitation and even a wintertime drought. The Köppen Climate Classification subtype for this climate is "Dfa"..
Education
Rensselaer has a public library, a branch of the Jasper County Public Library.
