Off-grid site report
Mercer County, IL
41.1995, -90.7487 · 745 ft elevationRead this before you act on anything below. This is my researched starting point for Mercer County, IL, not legal advice and not a guarantee. Rules change, and the deciding facts on any specific parcel (setbacks, perc results, overlay districts, deed restrictions, road frontage) live at the county or town office, not in any database. Before you buy land or build, confirm the current rules directly with the local zoning and health offices - the sources on this page tell you exactly who to call.
The local rulesMercer County, IL
Zoning & raw-land occupancy
Varies locallyMercer County has a countywide Zoning Ordinance (adopted 2023) administered by the county Zoning Office, but about 63% of municipalities in the county have their own separate zoning ordinances that can override the county rules within town limits. source
Dwellings, tiny homes & RVs
RestrictedManufactured/mobile homes are limited to specific zoned districts or approved conditional-use areas under the county ordinance and must sit on a state-approved permanent foundation; no specific county rule on tiny houses or RV residency was found, so confirm with the Zoning Office. source
Building permits & codes
Generally allowedThe county's Code Administrator issues building permits and Certificates of Occupancy for unincorporated land, requiring a site drawing with property-line distances; some towns like Viola run their own separate permitting. source
Septic & composting toilets
Generally allowedThe Mercer County Health Department administers septic permitting under the statewide IDPH Private Sewage Disposal Code, through a soil evaluation followed by a permit to construct; composting toilets are allowed under the state baseline but confirm local acceptance with the Health Department. source
Greywater reuse
Unclear - verifyNo Mercer County or Illinois state rule specifically addressing residential greywater reuse was found; this appears to fall under Health Department discretion, so ask the Mercer County Health Department directly.
Rainwater harvesting
Unclear - verifyNo Mercer County ordinance or state rule specifically authorizing or restricting rainwater harvesting was found; it's not confirmed how the county treats it.
Private wells & water rights
Generally allowedThe Mercer County Health Department handles well permitting and inspection as an agent of the Illinois Department of Public Health under the state Water Well Construction Code.
Living disconnected from utilities
Unclear - verifyNo explicit county ban on going off-grid from electric or water utilities was found, but a habitable dwelling still needs a compliant septic permit and, often, a Certificate of Occupancy from the county. source
Sun30-year normals
- Peak-sun hours, annual average
- 4.7 hrs/day
- Worst month (sizes an off-grid array)
- 3.1 hrs/day
- Yearly output per 1 kW of panels
- 1,369 kWh
JFMAMJJASOND
Weather1991-2020
- Precipitation
- 37 in/yr
- Heating degree days
- 6,565 (cold)
- Frost-free season
- Apr 25 to Oct 11
How far help isstraight-line
- Hospital
Genesis, Aledo - 0.7 mi
- Fire station
Aledo Fire Department - 0.1 mi
- Hardware store
B & B Hardware and Rental - 19.2 mi
- Grocery
Mercer Market - 0.9 mi
From OpenStreetMap. Road miles will be longer, often much longer in hill country.
Plan this spot
These open with this location's real numbers already filled in (ZIP 61231).
Size a solar systemHeat loss & insulationFirewood per winterRainwater harvestGarden sizePanel tilt
Looking at a specific parcel in Mercer County, IL?The rules above are the jurisdiction. The land check runs the parcel itself: flood zone, soils and septic suitability, wetlands, slope, access, climate, and these verdicts, from a parcel number or coordinates.
Check a parcel →Share or save this report:New report
Sources: US Census Bureau geocoder; NLR PVWatts v8 (solar); NOAA NCEI 1991-2020 climate normals (nearest station) or Open-Meteo (ZIP-centroid) for weather; Open-Elevation; OpenStreetMap contributors. Public data retrieved Aug 22, 2026; agencies update their layers on their own schedules. Planning data, not a survey or legal advice.
New here, or not sure where this fits? Start here walks through the whole thing in order.