Semiquincentennial: a word so rare my computer’s spellchecker underlined it in red. Among a national observance of the 250th anniversary of the Declaration of Independence, a few thoughts about Illinois: With statehood achieved in December 1818, Illinois has officially existed for almost 208 of the country’s 250 years, or 83%. The U.S. Constitution is only 237 years old, and it wasn’t quite 30 when Illinois joined the Union as the 21st state.