There were 753 households out of which 33.1% had children under the age of 18 living with them, 57.6% were married couples living together, 8.2% had a female householder with no husband present, and 30.7% were non-families. 27.1% of all households were made up of individuals and 12.9% had someone living alone who was 65 years of age or older. The average household size was 2.40 and the average family size was 2.91.
In the city the population was spread out with 26.3% under the age of 18, 8.3% from 18 to 24, 27.4% from 25 to 44, 23.5% from 45 to 64, and 14.5% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 92.5 males. For every 100 females age 18 and over, there were 87.3 males.
The median income for a household in the city was $39,837, and the median income for a family was $50,819. Males had a median income of $33,679 versus $25,256 for females. The per capita income for the city was $18,518. About 3.1% of families and 5.6% of the population were below the poverty line, including 4.9% of those under age 18 and 7.8% of those age 65 or over.
Monroe is home to Monroe Elementary School and PCM Community High School. The school district is composed of Prairie City and Monroe, and to a lesser extent, Otley, Resoner, and Vandalia.