St. Clair County, IL Water Table Trend
St. Clair County's groundwater trend, from USGS's own readings
St. Clair County's representative monitoring well shows depth to water holding roughly steady, a fitted trend of 0.3 ft per decade over 22 years of readings.
One well stands in for St. Clair County's whole aquifer here, the honest simplification every page on this site carries.
What the well actually measured
The most recent reading put water 9 ft below land surface. Readings span 2004-10-05 to 2026-06-11, 18 measurements from USGS well USGS-383321089594601 (1n8w-9.6h1), part of the National Water Information System. The qualifying bar and the OLS fit behind this trend are documented in the methodology guide.
Where St. Clair County ranks
Of the 1,449 US counties with a usable trend, St. Clair County ranks 447th from fastest-rising to fastest-declining, 1 is the fastest-rising water table measured, 1449 the fastest-declining. About 251,149 people live in St. Clair County, Illinois. See the fastest-moving counties guide for how St. Clair County stacks up against the most extreme cases nationally.
A dropping table says nothing about water quality
Whether St. Clair County's water table is rising or falling is independent of what's actually in the water. Depletion can concentrate naturally-occurring minerals, so it's worth checking directly with a water test rather than assuming a depth trend says anything about quality.