Research · updated 2026-08-20 · download the county-level CSV
Illinois Well Depth & Drilling Cost Index
Drilling a private water well in Illinois means paying by the foot — so the two questions every well owner asks are how deep and how much. We computed both for all 102 counties with enough records to be reliable, from 305,166 official ISGS well records.
Statewide, the median well reaches 140 ft, and a complete system — drilling, casing, pump, pressure tank, and hookup — typically runs $9,000–$15,000. But the county spread is large:
Deepest counties to drill in Illinois
| County | Median depth | Typical depth range | Complete system |
|---|---|---|---|
| Mercer | 395 ft | 123 ft–470 ft | $23,640–$39,400 |
| Hamilton | 298 ft | 160 ft–377 ft | $21,300–$35,500 |
| Henry | 275 ft | 160 ft–450 ft | $21,000–$35,000 |
| Union | 250 ft | 147 ft–392 ft | $17,820–$29,700 |
| Carroll | 240 ft | 170 ft–329 ft | $17,880–$29,800 |
Most expensive counties to drill in Illinois
| County | Complete system | Drilling & casing only | Median depth |
|---|---|---|---|
| Mercer | $23,640–$39,400 | $9,850–$25,610 | 395 ft |
| Grundy | $21,600–$36,000 | $9,000–$23,400 | 168 ft |
| Kendall | $21,600–$36,000 | $9,000–$23,400 | 235 ft |
| Hamilton | $21,300–$35,500 | $8,875–$23,075 | 298 ft |
| Henry | $21,000–$35,000 | $8,750–$22,750 | 275 ft |
Download the full county table (CSV)
How to read this
- Depth is measured; cost is modeled. Depths are the median of recorded drilled depths per county. Cost applies published Illinois per-foot drilling rates to that local median depth — a planning estimate, not a quote. Actual bids vary with geology, casing, site access, and water depth.
- Counties below 30 records are excluded so a thin sample can't produce a misleading superlative.
- Records are drilling events from the state database, which include some replacement and abandoned wells; deeper counties reflect real local geology (bedrock, aquifer depth).
Sources & methodology
- Illinois well records: ISGS (refreshed weekly; see our general methodology).
- Percentiles (p25/median/p75) computed per county; cost from published per-foot rate ranges applied to the local median depth.
The county table is free to use with attribution to Illinois Well Data (illinoiswelldata.com). For a specific county, a custom cut, or the underlying records, email — usually same-day.
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