Winnebago County, IL Water Table Trend
Winnebago County's groundwater trend, from USGS's own readings
Winnebago County's long-term well puts the trend at 26.8 ft per decade, rising, getting shallower over time, based on 10 measurements since 1986.
This is one representative well, not a county-wide survey, the same grain limit every page here discloses.
Winnebago County's source well, in detail
Depth to water at the last reading was 45 ft below land surface. Readings span 1986-04-16 to 2020-06-22, 10 measurements from USGS well USGS-421834089213501 (27n10e-29.1d1), part of the National Water Information System. The qualifying bar and the OLS fit behind this trend are documented in the methodology guide.
How Winnebago County compares nationally
Winnebago County sits at rank 6th of 1,449 ranked counties, ordered rising-to-declining, so a low number means a rising water table and a high one means fast decline. Winnebago County, Illinois is home to about 283,790 people. See the fastest-moving counties guide for how Winnebago County stacks up against the most extreme cases nationally.
Depth and quality are separate questions
This page answers a depth question, not a quality one. A well in Winnebago County can be stable in depth and still worth testing for quality, or declining and still test clean, the two are measured separately, and only a direct test settles the second one.