Buying Land in Washington County, Missouri

Zoning and building permits: unconfirmed for unincorporated land

Missouri's county zoning authority under RSMo Chapter 64 is opt-in, and this research pass did not turn up a public zoning map, zoning ordinance, or standing planning/zoning department specifically operated by Washington County for unincorporated land. Washington County appears as a member county of the Meramec Regional Planning Commission, a multi-county regional body covering several Ozark-region counties, but membership in a regional planning commission is not the same thing as the county itself having adopted zoning -- it's a coordination and technical-assistance relationship, not a land-use control. Given the uncertainty, treat this as genuinely unconfirmed rather than assuming either a zoning process or a zoning-free posture, and call the County Commission directly (102 N. Missouri Street, Potosi; (573) 436-7704) before making assumptions about a specific parcel.

Incorporated cities within the county, including Potosi (the county seat), may administer their own local codes independent of whatever does or doesn't apply to unincorporated county land -- if the parcel you're evaluating sits inside or near a city's limits, check with that city directly as well.

The Old Lead Belt: three centuries of mining, and what it means for well water today

Washington County is the historic heart of Missouri lead mining -- extraction here dates back to the early 1700s under French colonial settlement, making it one of the oldest continuously worked mining districts in North America, and the district went on to produce millions of tons of lead over three centuries of mining, milling, and smelting. That long history left elevated levels of lead, arsenic, barium, and cadmium in soil, sediment, surface water, and groundwater across a wide area, and -- as has happened elsewhere in Missouri's lead-mining counties -- some residents unknowingly purchased lead-contaminated mine gravel for use as fill, driveway material, and even playground surfacing.

EPA's response is organized as the Washington County Lead District (WCLD), covering four separate National Priorities List Superfund sites: Furnace Creek, Old Mines, Potosi, and Richwoods. The Old Mines site alone covers roughly 90 square miles in the northeastern part of the county. The Potosi, Old Mines, and Richwoods sites were added to the NPL in March 2008, with Furnace Creek investigated separately. This is not a closed chapter: soil excavation was actively underway at both the Old Mines and Potosi sites as of spring 2025, with a private engineering firm (EA Engineering, Science, and Technology) as the remediation contractor, and cleanup consists of excavating contaminated soil and gravel, replacing it with clean fill, and reestablishing vegetative cover.

The detail that matters most for a land buyer, though, is drinking water. Since 2006, more than 4,800 private domestic wells have been tested across the Washington County Lead District, and roughly one in seven has come back contaminated with lead and/or other heavy metals. In response, EPA signed an Interim Record of Decision in 2022 selecting point-of-use (POU) water treatment systems as an interim remedy for qualifying contaminated wells, paired with health education and institutional controls, while the agency continues a remedial investigation and feasibility study aimed at a final remedy for the underlying aquifer. At the Old Mines site alone, roughly 181 private wells qualified for POU treatment units. Testing and remediation of qualifying wells and yards is provided at no cost to the property owner.

What to check before buying, plus septic, assessor, and GIS resources

If a parcel you're considering has an existing well, ask directly whether that well has been tested through the Washington County Lead District program, and if so, what the result was -- a POU treatment system already installed is a meaningful fact to know about before you buy, and an untested well near any of the four site boundaries (Furnace Creek, Old Mines, Potosi, or Richwoods) is worth testing yourself before closing. If you'd need to drill a new well, ask a local well contractor and Missouri DNR whether the specific parcel's location has any known groundwater contamination history. This is a case where checking a parcel's Superfund-site proximity is at least as important as checking its flood-zone status elsewhere in the state -- see our dedicated well-water page for this county for a closer look at how to check a specific parcel and what a POU system does and doesn't cover.

Septic permits run through the Washington County Health Department (520 Purcell Drive, Potosi; (573) 438-2164), following the standard statewide Chapter 701 OWTS framework. For parcel research, the Washington County Assessor's Office ((573) 438-4992) maintains the county's roughly 25,600 parcel records with GIS mapping available through the county's ArcGIS web viewer, and the Recorder of Deeds (102 N. Missouri Street, Potosi; (573) 438-6111) holds deed, easement, and plat history. The county's Floodplain Administrator, Matthew Hart ((573) 438-3635), handles FEMA flood-zone questions and floodplain development permits for unincorporated land. MU Extension in Washington County (113 N. Missouri Street, Potosi; (573) 438-2671) offers general extension programs, though this research pass found its currently listed staff focused on nutrition and family-education programming rather than a dedicated agronomy specialist -- worth a direct call if you need soil or forage testing referrals.