Illinois

Buying Land in Putnam County, Illinois

Putnam County, seat Hennepin, is Illinois's smallest county by both land area and population -- and, as of an April 2026 EPA permit, home to a large carbon dioxide sequestration project tied to a Hennepin ethanol plant. That project puts Illinois's new pore-space and carbon-storage law directly into play here, on top of the county's own 2016 zoning ordinance.

Illinois's Smallest County -- 166 Square Miles, on the Illinois River

Generally favorable

Putnam is documented as the smallest Illinois county by both land area and population -- and, in a genuine historical reversal, it was formed in 1825 as the LARGEST county in the state before giving up land to form Bureau (1836), Marshall, and Stark Counties (1839). Its Hennepin courthouse, built in 1839, is reportedly the oldest courthouse still in use in Illinois.

A 2016 Zoning Ordinance, Recently Amended for Wind and Solar

Generally favorable

Putnam County adopted its current Zoning Ordinance on May 9, 2016, with dedicated sections for commercial and private wind energy systems and utility solar; the County Board amended those provisions in May 2023 to align with Illinois's statewide siting standards. A special-use permit for a commercial energy project requires a Planning Commission hearing and County Board approval.

A New Carbon Dioxide Sequestration Well Near Hennepin

Case-by-case / verify locally

In April 2026, the EPA approved a Class VI CO2 injection-well permit for Marquis Carbon Injection LLC, allowing injection of up to 1.5 million metric tons of carbon dioxide a year for six years into rock roughly 3,094 feet underground near Hennepin. This is a genuinely new kind of land-use question for Putnam County landowners -- see our dedicated page on what Illinois's pore-space and carbon-storage law means for a specific parcel.

The smallest county in Illinois -- and once the largest

Putnam County covers just 166 square miles and is documented as Illinois's smallest county by both land area and population -- a genuinely unusual status among the state's 102 counties. It's also a story of dramatic historical shrinkage: when Putnam County was carved out of Fulton County in 1825, it was, at the time, the LARGEST county in Illinois. The county gave up land to form Bureau County in the winter of 1836, then both Marshall and Stark Counties in early 1839, reaching its current small footprint by that year. The county seat, Hennepin, sits directly on the Illinois River, and its 1839 courthouse is reportedly the oldest courthouse building still in active use anywhere in the state.

None of this changes how land-use rules work here, but it's genuinely useful context: a county this small and this rural runs lean on staff and infrastructure, so confirming details directly with county offices -- rather than assuming a larger county's norms apply -- is worth the extra step.

Zoning: a 2016 ordinance, amended for Illinois's statewide wind/solar rules

Putnam County adopted its current Zoning Ordinance on May 9, 2016, administered through the county's Zoning & Floodplain Office. The ordinance includes dedicated sections covering commercial Wind Energy Conversion Systems (WECS), private WECS, and Utility Solar Energy Systems, in addition to standard use, setback, and lot-size provisions for unincorporated land. A commercial wind or solar project requires a special-use permit, which in turn requires a public hearing before the county's planning commission and final approval from the County Board.

Putnam County reportedly imposed an earlier moratorium on new wind-energy project approvals before Illinois enacted Public Act 102-1123 in January 2023, which set statewide floors and ceilings for county wind and solar siting rules and barred outright moratoriums. In May 2023, the County Board unanimously approved a text amendment updating its wind and solar regulations for unincorporated Putnam County to align with that statewide framework -- confirm the county's current, specific setback and siting requirements directly with the Zoning & Floodplain Office before relying on this summary for a wind or solar lease decision.

A new kind of land-use question: carbon dioxide sequestration near Hennepin

In April 2026, the U.S. EPA approved a Class VI underground-injection-control permit for Marquis Carbon Injection LLC -- a project tied to the Marquis Energy ethanol plant in Hennepin -- allowing the company to inject up to 1.5 million metric tons of carbon dioxide per year, for six years, into a rock formation roughly 3,094 feet below ground, with about 963 feet of confining rock (including a 404-foot shale-and-carbonate layer) separating the injection zone from the deepest underground source of drinking water. EPA's approval requires monitoring during the six years of injection and for twelve years afterward. The project has drawn documented public opposition, including multiple Sierra Club Illinois chapter articles raising concerns about groundwater protection and the broader Marquis ethanol-plant expansion.

This intersects directly with a genuinely new area of Illinois property law: the 2024 SAFE CCS Act formalized that title to underground "pore space" stays with the surface landowner and cannot be severed from the surface estate, while also creating a "unitization" process letting a sequestration operator petition the state to bind in holdout landowners once it has secured rights from at least 75% of those affected. Separately, the Illinois Commerce Commission retains authority to grant eminent domain for CO2 pipeline easements, though new CO2 pipeline construction in Illinois is under a moratorium tied to federal pipeline-safety rulemaking. See our dedicated page on carbon-sequestration easements in Putnam County for what this could mean for a specific parcel's mineral and pore-space rights, whether or not that parcel sits anywhere near the Hennepin project itself.

Septic, assessor, and recorder contacts

Septic (private sewage disposal) and well permitting in Putnam County runs through the joint Bureau, Putnam & Marshall County Health Department, which issues well-sealing and sewage-disposal-system permits under the statewide IDPH Title 77 Part 905 framework and requires 48 hours' notice before a final sewage-construction inspection. Call ahead for the current list of licensed installers and pumper contractors.

The Putnam County Assessor's Office and County Clerk & Recorder's office are both located at 120 North 4th Street in Hennepin -- the 1839 courthouse building -- and handle property valuation, GIS/parcel mapping requests, and recorded deeds, easements, and plats for a specific parcel, including any pore-space lease or CO2-sequestration-related instrument that gets recorded against a property in the future.

What we could and couldn't confirm

Putnam County's size, population, and 1825-1839 formation/shrinkage history are corroborated via Wikipedia and multiple search-indexed genealogical/historical sources; the 1839 courthouse's status as Illinois's oldest still in use is drawn from a single search-indexed source and not independently cross-checked further. The 2016 zoning ordinance's wind/solar provisions and the 2023 board amendment are drawn from an EnergyZoning.org-hosted copy of the ordinance and Shaw Local reporting rather than a direct read of putnamil.gov, since direct WebFetch access to that domain was blocked by a network egress restriction throughout this research pass. The Marquis Carbon Injection Class VI well figures (1.5 million metric tons/year, six-year injection period, ~3,094-foot depth, 12-year post-injection monitoring, April 2026 approval date) are drawn from the EPA's own news release as indexed by search; direct WebFetch to epa.gov was blocked, so these figures reflect a search-indexed summary rather than a full verbatim read of the permit itself. The SAFE CCS Act's pore-space, unitization, and eminent-domain provisions are corroborated across multiple independent law-firm summaries and the enrolled bill text link, though this pass did not read the full bill text verbatim. This session's overall WebSearch budget was exhausted before a University of Illinois Extension office description specific to Putnam County could be located, so no Extension contact is listed here rather than guessed from a neighboring county's office.

Verify directly with: the Putnam County Zoning & Floodplain Office for current zoning and special-use-permit status on a specific parcel, the Bureau, Putnam & Marshall County Health Department for septic and well permitting, and an Illinois-licensed real estate or energy attorney for how the SAFE CCS Act's pore-space and unitization provisions apply to a specific parcel's mineral and subsurface rights

Who to Call Before Buying Land in Putnam County

Direct WebFetch access to putnamil.gov and bpmhd.org was blocked by a network egress restriction throughout this research pass, so department details reflect search-indexed content rather than a full verbatim read -- confirm current staff, hours, and fees directly before relying on this page for a specific parcel. This pass could not locate a University of Illinois Extension office description specific to Putnam County before this session's overall WebSearch budget was exhausted, so an Extension contact is omitted here rather than guessed.

Planning & Zoning