The Illiopolis plate. Relief from Copernicus GLO-30; rivers and lakes from USGS NHD; watersheds from the USGS Watershed Boundary Dataset; roads and city limits from Census TIGER 2024.
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Mostly sunny; warmer
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3.66 inches of rain fell in two days, the most for this week of the year since records began in 1893. The next wettest, 3.04 inches, fell in 1964.
Illiopolis’s center stands about 610 ft above sea level. Within three miles the land runs from 560 ft to 610 ft, a difference of 50 ft: nearly flat ground.
Under the town center the state geologic map shows Shelburn-Patoka Formations undivided (shale, limestone), from the Late Pennsylvanian, 304 to 307 million years old.
The section below crosses 2 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 64×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Shale, limestone. Age: Late Pennsylvanian, 304 to 307 million years old. About 19 mi of the line.
Shale, sandstone, limestone. Age: Late Pennsylvanian, 304 to 307 million years old. About 5 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
Heights from Copernicus GLO-90 (a surface model: it includes buildings and tree canopy); summits from USGS GNIS; rivers from USGS NHDPlus HR; rock from the USGS State Geologic Map Compilation.
A raindrop that lands in Illiopolis reaches the Gulf of America by way of the Sangamon, the Illinois and the Mississippi: about 1,390 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Illiopolis; river miles along the main stem, rounded.
Illiopolis has a hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 20° in January. A normal year brings about 14 inches of snow; with the rain, that comes to about 40 inches of water.
On November 14 Illiopolis normally reaches 51° and falls to 35°. The record high is 77°, in 1931; the record low 8°, in 1986. The most rain on this date, 1.51 in, fell in 1957.
Normals 1991–2020 and records since 1893 at Decatur Wtp, 16 miles east. NOAA, through RCC-ACIS.
