Rockhounding in Grundy County, Illinois

3 mapped rockhounding spots in Grundy County. Most commonly produces concretions with fossils, fern fossils, fossils, marcasite.

Grundy County rockhounding photos

Representative spot and material photos from this county, shown where verified public image records are available.

1 photo

Fossiliferous ironstone (siderite) concretion holding a fern fossil, of the type collected from the Mazon Creek beds at the Pit 11 / Mazonia-Braidwood area, Grundy County, Illinois — Mazonia-Braidwood State Fish & Wildlife Area (Pit 11)Grundy County, Illinois

Minerals reported in Grundy County

Standout in Grundy County

Hand-picked spot in Grundy County, chosen for unusual mineralogy or documented public access. Each card opens the full coordinates and access notes.

Top pick
Mazonia-Braidwood State Fish & Wildlife Area (Pit 11)
Public
Grundy County
The Mazonia unit preserves the reclaimed spoil of the old Pit 11 coal strip mine, the source of the world-famous Mazon Creek fossil biota and its soft-bodied preservation inside siderite (ironstone) concretions.
Concretions With Fossils, Siderite, Tully Monster, Fern Fossils

Spots in Grundy County

Spot	Minerals	Coordinates	Access
East BrooklynSouth Kankakee Road	Marcasite Pyrite	41.1666, -88.2450	Public
Mazon River	Fossils	41.2934, -88.3667	Public
Mazonia-Braidwood State Fish & Wildlife Area (Pit 11)Illinois Route 53	Concretions With Fossils Siderite Tully Monster Fern Fossils	41.1975, -88.2708	Public

Neighboring counties in Illinois

Adjacent rockhounding counties, ranked by how close their centroids sit to Grundy County. A natural extension if Grundy County is already on your trip plan.

Across the state line from Grundy County

Rockhounding counties in neighboring states within driving range. Geology rarely respects state borders — these are often the closest mapped spots you can reach without going deeper into Illinois.

Grundy County FAQ

Where can I rockhound in Grundy County, Illinois?+

RockHoundR tracks 3 rockhounding spots in Grundy County. Each entry below has coordinates, mineral notes, and access type. Always confirm local rules before collecting.

What rocks and minerals are common in Grundy County?+

Spots in Grundy County most often produce Concretions With Fossils, Fern Fossils, Fossils, Marcasite, Pyrite. Individual spots can vary widely.

Are these Grundy County rockhounding spots on public land?+

Most spots in this list are tagged public, but access can change with seasons, claims, and local closures. Always verify before driving out — links in the app open the right BLM, USFS, or county pages.

Plan a Grundy County rockhounding trip

Open RockHoundR to see these spots on the map alongside land overlays, weather, geology, and your saved finds.