US Land Life

Missouri

Buying Land in Mercer County, Missouri

Mercer County sits on the Iowa border in far north-central Missouri, seat Princeton, and it's one of the state's smallest counties by population -- which shapes everything from who answers the phone at the courthouse to how little regulatory apparatus stands between a landowner and a given use of the land.

No County Zoning Anywhere in Unincorporated Mercer County

Case-by-case / verify locally

Mercer County has not adopted county-wide planning and zoning under RSMo Chapter 64, so there's no zoning map, no zoning department, and generally no conditional-use hearing standing between a landowner and most uses of unincorporated land. Princeton, the county seat, requires a building permit for construction within city limits but has not adopted its own building code, so even inside the city the regulatory floor is thinner than in a typical Missouri town. Confirm with the County Commission (Mercer County Courthouse, 802 E. Main, Princeton, MO 64673; (660) 748-3425) whether the county has separately adopted Chapter 64 subdivision regulations, since that's a distinct authority from zoning that public sources didn't settle for us.

Septic Runs Through the Mercer County Health Department

Generally favorable

Onsite wastewater treatment system (septic) permits for unincorporated Mercer County are handled by the Mercer County Health Department (305 W. Main, Princeton, MO 64673; (660) 748-3630) under the statewide OWTS construction-permit framework administered by the Missouri Department of Health and Senior Services (Chapter 701 RSMo) -- the standard setup for a rural Missouri county without its own environmental-health ordinance layered on top. Plan for a soil evaluation before you commit to a building site.

A Very Small, Very Agricultural County -- Land-Use Pressure Is Low but So Is Infrastructure Density

Case-by-case / verify locally

At 3,538 residents (2020 census) across 455 square miles, Mercer County is Missouri's second-least-populous county, and its economy runs on row crops, cattle, and hay. That means little competition for land and few land-use conflicts to navigate, but it also means fewer paved roads, thinner utility infrastructure in outlying areas, and a courthouse staff that wears multiple hats -- budget more time for in-person visits and phone calls than you would in a county with a dedicated planning staff.

No zoning, and a genuinely small government to match

County-level zoning in Missouri only exists where a county has affirmatively adopted it under RSMo Chapter 64, and Mercer County has not done so. Unincorporated land here carries no zoning classification and no conditional-use permit process; questions about what you can build or run on a given parcel route to the County Commission rather than to a planning and zoning office, because there isn't one. Princeton, the county seat and largest town (population just over 1,000), requires a building permit for work inside city limits but has not itself adopted a formal building code, so the regulatory floor stays thin even where a permit is required.

That absence of zoning cuts both ways for a buyer. On one hand, there's no rezoning fight or use-variance hearing standing between you and most farm, residential, or outbuilding uses of a rural parcel. On the other, there's also nothing stopping a neighboring parcel's use from changing without notice or hearing -- if the row-crop field next door matters to your plans, that assurance needs to come from a private agreement or deed restriction, not from the county. It's worth asking the County Commission directly whether Mercer County has adopted separate Chapter 64 subdivision regulations (plat review, minimum road standards, and drainage requirements for new subdivisions are a distinct authority from zoning that some non-zoned Missouri counties still keep on the books) -- we could not confirm that either way from public sources during this research pass.

Septic and wells: the standard rural Missouri framework applies

Onsite wastewater treatment system permits for a rural Mercer County parcel go through the Mercer County Health Department (305 W. Main, Princeton, MO 64673; (660) 748-3630), which administers the state OWTS construction-permit process under Missouri Department of Health and Senior Services rules and Chapter 701 RSMo. As in most rural Missouri counties, plan on a site and soil evaluation before a construction permit issues, and budget for the system to fit the specific soil conditions of your parcel rather than assuming a standard trench system will work on every lot.

Private wells are a state, not a county, matter: Missouri DNR sets well construction standards and certifies well contractors statewide, and a domestic well in Mercer County follows those same rules rather than a separate county permit. Landowners may legally install their own well without a contractor's permit but must still meet DNR construction standards, and a licensed contractor doing paid work needs a DNR well construction permit and must file a completion report with the state within 60 days.

Agriculture, a small Amish community, and Lake Paho

Agriculture is the backbone of Mercer County's economy, with row crops (corn and soybeans), cattle, and hay production supporting most of the county's family farms. The county also has a documented Amish settlement founded in 2005 that straddles the Mercer County, Missouri / Decatur County, Iowa line, according to Amish-settlement tracking sources -- a smaller and more recent community than the well-known Spickard/Princeton-area settlement, which is actually centered in neighboring Grundy County rather than Mercer County itself, so don't conflate the two if you're researching either one.

For recreational and hunting-interest buyers, Lake Paho Conservation Area sits roughly in the center of the county: a 273-acre lake built by the Missouri Department of Conservation in the late 1940s with local financial support, opened to public fishing in 1951, and surrounded by rolling native-prairie terrain (Indian grass, compass plant, wild indigo). It's public land, not something you'd buy, but it's a genuine local amenity worth knowing about if you're evaluating a nearby parcel for recreational value. General claims about Mercer County having exceptional trophy whitetail hunting show up in land-listing marketing copy, but we didn't find county-specific data (harvest records, Boone and Crockett entries tied specifically to Mercer County) to back that up as more than generic regional marketing, so treat those claims with appropriate skepticism rather than as a documented differentiator.

Who to Call Before Buying Land in Mercer County

Mercer County has no zoning or planning department, so the County Commission is the practical first contact for most unincorporated land-use questions, with the Health Department handling septic and DNR handling wells at the state level. We could not confirm a direct GIS/parcel-viewer contact or a separate email for most of these offices from public sources -- use the phone numbers and websites above, or the county courthouse directly at (660) 748-3425.

Other

Mercer County Commission

General county governance and the first call for any land-use question in unincorporated Mercer County given the absence of a zoning department.

Phone: (660) 748-3425Official website →

Environmental Health

Mercer County Health Department

Onsite wastewater treatment system (septic) permits and general environmental health questions.

Phone: (660) 748-3630Official website →

Septic / Onsite Wastewater

Mercer County Health Department (Environmental Health)

OWTS construction permits, required soil evaluations, and septic system compliance.

Phone: (660) 748-3630Official website →

Wells / Private Water

Missouri Department of Natural Resources -- Wells and Drilling Program

Private well construction rules and certified well-contractor requirements statewide, including Mercer County.

Official website →

Floodplain / Stormwater

Mercer County Emergency Management (Floodplain Administrator)

FEMA flood-zone questions and floodplain development permits for unincorporated Mercer County.

Phone: (660) 748-3425Official website →

Assessor / Property Tax

Mercer County Assessor

Assessed value, GIS/parcel maps, and property tax questions for a specific parcel.

Phone: (660) 748-3511Official website →

Recorder / Clerk / Land Records

Mercer County Recorder of Deeds

Recorded deed, easement, and plat history for a specific parcel.

Phone: (660) 748-4335Official website →

Agricultural Extension

MU Extension in Mercer County

Agricultural, soil-testing, and land-management guidance for county landowners.

Phone: (660) 748-3315Official website →

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Sources

  1. ADU Regulations In Missouri (2026 Guide) — Zook Cabins (accessed 2026-09)
  2. Tiny Home Regulations In Missouri (2026 Guide) — Zook Cabins (accessed 2026-09)
  3. Mercer County Health Department — Missouri Department of Health and Senior Services (accessed 2026-09)
  4. Mercer County Health Department (profile PDF) — Missouri Department of Health and Senior Services (accessed 2026-09)
  5. Mercer County Health Department (official site) — Mercer County Health Department (accessed 2026-09)
  6. On-site Septic Systems and Subdivisions — Missouri Department of Natural Resources (accessed 2026-09)
  7. Wells and Drilling — Missouri Department of Natural Resources (accessed 2026-09)
  8. Well Installation Frequently Asked Questions (FAQ) - PUB2193 — Missouri Department of Natural Resources (accessed 2026-09)
  9. Mercer County — Missouri State Emergency Management Agency (accessed 2026-09)
  10. Mercer County Assessor — Mercer County, Missouri Government (accessed 2026-09)
  11. Mercer County, MO, Recorder of Deeds — Mercer County, Missouri Government (accessed 2026-09)
  12. Mercer County | MU Extension — University of Missouri Extension (accessed 2026-09)
  13. Mercer County — Missouri Association of Counties — Missouri Association of Counties (accessed 2026-09)
  14. FAQ | City of Princeton Missouri — City of Princeton, Missouri (accessed 2026-09)
  15. Building Permits & Inspections | City of Princeton Missouri — City of Princeton, Missouri (accessed 2026-09)
  16. Lake Paho Conservation Area — Missouri Department of Conservation (accessed 2026-09)
  17. Missouri Amish Guide (60+ Communities) — Amish America (accessed 2026-09)
  18. Missouri Is America’s #7 Amish State — These Are Its 10 Biggest Communities — Amish America (accessed 2026-09)
  19. Mercer County, Missouri | United States Counties Wiki — Countypedia (Fandom) (accessed 2026-09)

Last reviewed 2026-09