The first European explorers to reach Illinois were the Frenchmen Marquette and Jolliet (or Joliet), in 1673. French priests established Catholic missions starting in 1675. The region remained under French control until 1763, when it was ceded to Britain.
The British operated it until the Revolution. In 1778, General George Rogers Clark captured Kaskaskia and took possession of the entire Illinois territory for the United States. After the war ended, American control was officially recognized.
Initially, Illinois was included with Indiana, but in 1809, it was reorganized as an independent territory. The first settlement at what was to become Chicago was a log cabin built in 1779.
Fort Dearborn was established on the site, which was the scene of a bloody massacre of settlers by the Potawatomi Indians in 1812. The population grew nevertheless, and Illinois was admitted as the 21st state in 1819. At first, settlement was limited to the southern third of the state, but the northern boundary was extended to its present line with Wisconsin, which brought Chicago into the state.
The first state capital was established at Vandalia, in 1820. The population grew rapidly after the opening of the Erie Canal. A new capital was discussed in the 1837 legislature and Springfield was chosen. Canals and railroads allowed Illinois farmers to ship their produce to the East in greater and greater quantities.
Before the Civil War, Illinois received national publicity due to the debates between Stephen Douglas and Abraham Lincoln. The debates took place during the campaign for the U.S. Senate, which Lincoln lost. However, his positions gained him a national reputation that led to his being elected president, in 1860.
After the Civil War, Illinois grew rapidly as a manufacturing center. The state adopted some of the country's most progressive legislation during the period of reform.
Illinois also played a prominent role in the development of atomic energy. Enrico Fermi demonstrated the world's first controlled nuclear reaction in Chicago, in 1942. The Argonne National Laboratory near Chicago, plays a leading role in finding industrial uses for atomic energy.