Johnson County, IA Water Table Trend
Johnson County's groundwater trend, from USGS's own readings
Johnson County's long-term well puts the trend at 0.1 ft per decade, holding roughly steady, based on 917 measurements since 1941.
This is one representative well, not a county-wide survey, the same grain limit every page here discloses.
Johnson County's source well, in detail
Depth to water at the last reading was 15.3 ft below land surface. Readings span 1941-10-24 to 2026-07-10, 917 measurements from USGS well USGS-414315091252002 (080n05w22cbcb2 1941elmira Depot 5 Iacrn-4), part of the National Water Information System. The qualifying bar and the OLS fit behind this trend are documented in the methodology guide.
How Johnson County compares nationally
Johnson County sits at rank 577th 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. Johnson County, Iowa is home to about 160,080 people. See the fastest-moving counties guide for how Johnson 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 Johnson 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.