Hamilton: Geode Digging in Hancock County, Illinois

Plan your visit

Generally open to casual rockhounding

County

Hancock County

State

Illinois

Nearest road

South 9th Street

Postcode

62341

Coordinates

40.38723, -91.34623

Coordinates are approximate. Confirm the exact ground in the RockHoundR app, where land overlays show which agency manages the area.

Land & collecting status

Generally open to casual rockhounding

Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig.

Access note: Geodes are found in creek beds and Mississippi River gravel reachable from public road bridges and river accesses, where the loose surface material below the ordinary high-water mark can be picked. Much of the surrounding ground is private farmland, so ask permission before crossing fields or digging into banks. Hancock County, west-central Illinois. Water is lowest in late summer and early fall.

Public-land rules vary by agency, season, and field office. The RockHoundR app pulls live BLM, USFS, NPS, and tribal overlays so you can see exactly which agency manages the ground at this spot.

Best time to visit Hamilton

Comfortable months (45 to 90°F highs)

Best months: March to November. Typical highs run 85°F in midsummer and 33°F in midwinter, with winter lows near 17°F.

Climate normals: NOAA 1991-2020 monthlies, KEOKUK L&D 19 station (2 mi away).

Geology at Hamilton

This spot sits on Warsaw Formation and Salem Limestone, mapped as limestone that formed roughly 345 to 330 million years ago. Limestone country like this is classic geode ground: cavities in the carbonate rock can line themselves with quartz or calcite crystals.

Mapped unit

Warsaw Formation and Salem Limestone

Age

345–330 Ma (Mississippian)

Rock types

limestone

Elevation

560 ft

Geologic mapping via Macrostrat and the underlying state geological survey maps (CC BY 4.0). Bedrock at the surface can vary within a mapped unit.

Sources & verification

Spot details combine the public RockHoundR location dataset, normalized mineral labels, agency land-status checks in the app, and community submissions. Coordinates are approximate until verified in the field.

• Illinois State Geological Survey
• Illinois DNR site rules
• Shawnee National Forest
• Community submissions reviewed against published agency rules