According to the United States Census Bureau, the city has a total area of 3.9 square miles (10.0 km²), of which, 3.7 square miles (9.6 km²) of it is land and 0.2 square miles (0.5 km²) of it (4.90%) is water.
Shelbyville was founded in 1827 and named in honor of Isaac Shelby, hero of the Revolutionary War and Governor of Kentucky. The history of Shelbyville begins with Barnett Bone, a Tennessean who, in 1835, built a log cabin along the Kaskaskia River. His cabin eventually became the county courthouse. The first businesses were blacksmith shops, a general store and stage coach stop, and a grist mill.
The Army Corps of Engineers broke ground on the dam in 1963, and construction was completed in the early summer of 1970.
There were 2,133 households out of which 27.6% had children under the age of 18 living with them, 49.6% were married couples living together, 9.6% had a female householder with no husband present, and 36.9% were non-families. 33.1% of all households were made up of individuals and 16.9% had someone living alone who was 65 years of age or older. The average household size was 2.28 and the average family size was 2.89.
In the city the population was spread out with 23.0% under the age of 18, 8.3% from 18 to 24, 25.3% from 25 to 44, 21.5% from 45 to 64, and 21.9% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 91.2 males. For every 100 females age 18 and over, there were 87.6 males.
The median income for a household in the city was $32,458, and the median income for a family was $39,205. Males had a median income of $31,477 versus $18,710 for females. The per capita income for the city was $17,596. About 6.2% of families and 9.9% of the population were below the poverty line, including 10.2% of those under age 18 and 13.8% of those age 65 or over.
Shelbyville was also home to the well-known American Tonalist painter Robert Marshall Root (1863-1937), most famous for his painting of the Lincoln-Douglas Debate in Charleston, Illinois held in 1856. Root was the subject of a large cataloging project and art exhibition in 2006, and the topic of the James W. Moore lecture at Millikin University.
Another famous painter, Charles Lloyd Heinz (1884-1953) was born and lived in Shelbyville. He studied under Robert Marshall Root and was most famous for his work in and around Cape Cod and Provincetown, Massachusetts.
Samuel Wheeler Moulton (1821-1905) is considered the father of public education in Illinois, and lived in Shelbyville from 1849 until his death in 1905. Moulton was president of the board of education for the State of Illinois from 1859-1876. He also served in the Illinois General Assembly (1852-1859) and the United States House of Representatives (1865-1867, 1881-1885). He is buried in Shelbyville, and the middle school in Shelbyville is named in his honor. Additionally, built in 1912, Illinois State University renamed the former Metcalf Hall in honor of Moulton in 1962.
Anthony Thornton (1814-1904) was born in Kentucky but upon graduation from Miami University, he made his way to Shelbyville and set up a law practice. Thornton had a long and distinguished military, political and judicial career, as a major in the United States Army in the Mexican-American War, member of the Illinois House of Representatives (1851-1852), member of the United States Congress (1865-1867) and a justice of the Illinois State Supreme Court (1870-1873). He also debated Abraham Lincoln in Shelbyville in 1856, an historic moment recreated by local artist Robert Marshall Root in 1913 that now hangs in the Shelby County Courthouse.
The dishwasher was invented in Shelbyville in 1886, by Josephine Garis Cochran, and received patent #355139. She founded a company to manufacture her invention which later became KitchenAid Corporation. A monument to that effect stands in front of her former home in Shelbyville.
Another Shelbyville invention, the first commercial pick-up bailer, was designed and developed by Raymore McDonald, as conceived and financed by Horace M. Tallman and his two sons, Leslie and Gentry. These balers were marketed for many years by the Ann Arbor Machine Company of Shelbyville. This concept of field processing of farm forages made a significant contribution to the efficiency and economy of harvesting in the world's agriculture. This basic field pick-up mechanism has been used in over 15 million balers. The American Society of Agricultural and Biological Engineers designated Shelbyville as an historical landmark of agricultural engineering, of which there are only 47 in the entire United States. Mr. Tallman's home has been restored and is on the National Register of Historic Places.
Shelbyville is also home to Sparks College, a nationally-renown business trade school, founded in 1908.
Shelbyville is the rival city to Springfield in The Simpsons.