Rochester is a village and suburb of Springfield in Sangamon County, Illinois, United States. As of the 2020 census, Rochester had a population of 3,863. The village was settled in 1819, and is located in Rochester Township.

Rochester is part of the Springfield, Illinois Metropolitan Statistical Area.

Rochester is located four miles (6.4 km) outside Springfield, Illinois, down Illinois State Route 29. The village is exit 96A off Interstate 55.

According to the 2010 census, Rochester has a total area of 2.431 square miles (6.30 km²), of which 2.43 square miles (6.29 km²) (or 99.96%) is land and 0.001 square miles (0.00 km²) (or 0.04%) is water.

As of the 2020 census, Rochester had a population of 3,863. The median age was 41.1 years. 26.2% of residents were under the age of 18 and 18.9% of residents were 65 years of age or older. For every 100 females there were 92.2 males, and for every 100 females age 18 and over there were 89.4 males age 18 and over.

98.4% of residents lived in urban areas, while 1.6% lived in rural areas.

There were 1,460 households in Rochester, of which 37.0% had children under the age of 18 living in them. Of all households, 62.9% were married-couple households, 10.1% were households with a male householder and no spouse or partner present, and 22.9% were households with a female householder and no spouse or partner present. About 21.3% of all households were made up of individuals and 13.2% had someone living alone who was 65 years of age or older.

There were 1,509 housing units, of which 3.2% were vacant. The homeowner vacancy rate was 1.9% and the rental vacancy rate was 6.6%.