Methodology & sources

Every number on this site is computed from public records. This page shows the work.

Source data

All well records come from the Illinois State Geological Survey's water well records, the state's official archive of well logs filed since the 1800s (isgs.illinois.edu/groundwater/well-records). We refresh our copy weekly from the state's public data service. (305,166 well records at last refresh, 2026-08-20.)

Filters

• ISGS water wells; engineering, mineral and stratigraphic test borings, mine shafts, outcrops and monitoring wells are excluded, as are wells the survey records as plugged; depths 0-5,000 ft
• Static water level statistics use measurements 0–2,000 ft below ground surface; zero/blank values are treated as missing
• Yield statistics use reported flows/pump tests 0–5,000 gpm
• Records without a resolvable county are excluded from county pages
• Counties with fewer than 10 records are not published

Statistics

We report medians and interquartile ranges (25th–75th percentile) rather than averages, because well data is heavily skewed — a few very deep wells would distort an average. "Recent" figures cover wells completed since 2016. Driller tables count wells by the driller on logs filed since 2016.

Cost estimates

We do not collect quotes. Cost ranges apply published national per-foot rates to the local median depth — the local depth is what makes the estimate useful, and it comes from actual drilled wells nearby:

• Drilling + casing: $25–$65 per foot
• Complete system (pump, pressure tank, hookup): $60–$100 per foot

Rate sources (last checked 2026-06-11):

• HomeGuide — Well Drilling Cost (2026) — $25–65/ft drilling + casing; complete systems $3,000–15,000, most $5,500–9,000
• Angi — How Much Does Well Drilling Cost? (2026) — cross-check: drilling alone $15–25/ft; complete installation $25–65/ft
• The Well Guide — Well Drilling Cost (2026) — depth tables (e.g. 150 ft: $9,000–13,000 all-in); Mountain West/Pacific NW: $35–65/ft, systems $10,000–25,000
• the Illinois State Geological Survey water well records — all depth/static-water-level/yield figures are computed from ISGS records, not estimated

Estimates are planning figures, not quotes. Site access, geology, casing depth, and water treatment needs move real prices substantially.

Known data limitations

• Location accuracy varies by record: every Illinois water well record carries a mapped location, but the state files wells by section and township rather than by street address, so results show the records around a property rather than a single wellhead.
• Not every well is on record — older and hand-dug wells are under-represented.
• Some records contain filing errors; we propagate the official record as filed.

Corrections

If a number here looks wrong, email us (or reply to any report). Confirmed errors are corrected and logged on the changelog. In this niche one wrong number costs more trust than ten missing features — we'd rather show less and be right.

About

Illinois Well Data is an independent data publisher. We are not affiliated with ISGS, the State of Illinois, or any drilling company. Revenue comes from property reports and from connecting homeowners with licensed local drillers — never from selling rankings or placements in the statistics.