Most of the Illinois towns featured here sit on rivers, and floods destroyed or largely emptied four of them. Kaskaskia, the first state capital until 1819, was mostly destroyed in April 1881 when the Mississippi shifted into a new channel. After the Ohio River flood of 1937, much of Old Shawneetown's population moved several miles inland. After the Great Flood of 1993, Valmeyer rebuilt on the bluffs two miles east and left its old town site to fields. Cairo, where the Ohio meets the Mississippi, fell from 15,203 people in 1920 to 1,733 in 2020.
Inland, Millville in Jo Daviess County was bypassed by the Illinois Central Railroad in 1853 and 1854 and swept away by a flood in 1892. Vishnu Springs in McDonough County was a health resort that could be considered abandoned by the 1920s. Around Chicago, Orchard Place was dissolved for O'Hare Airport and Weston for Fermilab. What survives ranges from living villages with a few historic buildings to town sites with nothing above ground but a plaque.