Two parcels went up for sale near Spring Green this year within a few weeks of each other. Both were priced in roughly the same range per acre. One was a wooded ridge lot advertised for hunting and a future build site, the kind of ground that has never seen a plow. The other was a strip carved off the edge of an active cornfield, close enough to the village that a buyer could walk to the Wisconsin River in twenty minutes.
On paper, they looked like the same deal. They were not. One of those buyers is going to get a bill from a county treasurer that the other will never see, and the price per acre on the listing sheet had nothing to do with which one it would be. The village of Spring Green sits in Sauk County, but the broader river valley it anchors reaches into Iowa and Richland counties too, so which treasurer sends that bill, and how large it is, depends on exactly which side of a county line a parcel falls on.
The Charge That Never Makes The Listing
Wisconsin has taxed farmland at its agricultural use value, not its market value, since 1995. That is a real break for landowners who keep working the ground. But the law that created the break also built in a claw-back. When land that has been assessed as agricultural gets converted to residential, commercial, or another non-farm use, the county issues a one-time conversion charge under Wisconsin Statute 74.485, calculated on the gap between what that land would sell for on the open market and the artificially low value it has been taxed on.
The Department of Revenue's own guidance walks through the math with a simple example: if a county's average market value for agricultural land is $5,490 an acre and the average use value is $210 an acre, the gap is $5,280 an acre. That gap, not the purchase price, is what gets charged. The percentage applied depends on how much acreage changes use at once. Convert more than 30 acres and the rate is 5 percent of the gap. Convert 10 to 30 acres and it climbs to 7.5 percent. Convert fewer than 10, which is exactly the size most homesite buyers are looking at, and the rate jumps to 10 percent.
How The Same Gap Turns Into Very Different Bills
The percentage tiers matter because they apply to the same underlying number, so the per-acre charge for a small conversion can run double what a large one pays. Dane County's treasurer publishes a clean example of how this plays out:
| Acres converted | Rate applied to the market-use gap | Charge per acre |
|---|---|---|
| Fewer than 10 acres | 10% | $1,329 |
| 10 to 30 acres | 7.5% | $997 |
| More than 30 acres | 5% | $664 |
Sauk, Iowa, and Richland counties each run their own version of this table, and the dollar figure moves every time the Department of Revenue reissues its statewide report. The department publishes a full county-by-county breakdown annually, but pulling the wrong column from that report is easy to do, and the number for any single county is only good for one conversion year. The safest move for a buyer looking at Spring Green area land is a direct call to whichever county treasurer's office holds the parcel and a request for the current per-acre figure, rather than reading it off a chart built for a different year or a neighboring county.
Same Price Per Acre, Different Bill
Here is where the two Spring Green parcels split apart. General land listings around Spring Green have been averaging close to $23,000 an acre, a figure that covers everything from wooded ridge lots to small hobby parcels. Land specifically marketed as tillable farmland has been pricing much higher, closer to $59,950 an acre. That premium exists because active cropland produces income and carries a market value the state actually tracks for the conversion formula.
The wooded ridge parcel, the kind advertised for hunting and building rather than row crops, was almost certainly never classified as agricultural cropland in the assessor's system to begin with. Land that qualifies as productive forest, agricultural forest, or undeveloped is statutorily exempt from the conversion charge entirely, no matter how it gets used afterward. The cornfield-adjacent parcel is a different story. If it is still on the roll as Class 4 agricultural land, carving off even a modest homesite triggers the charge, and because homesites are almost always under 10 acres, it triggers at the highest rate.
The buyer paying more per acre for the tillable ground is, in a strange twist, often buying the parcel with less hidden exposure once the price premium is accounted for. The buyer who thought they got the bargain on the cheaper wooded lot may be the one who never owed anything. Price per acre tells you what the seller wants. It tells you nothing about what class of land you are actually buying.
Under the use-value law, sellers are required to give buyers written notice of whether the land has been assessed as agricultural, whether a conversion charge has already been assessed on it, and whether any deferral is in place. That notice is not optional paperwork. It is the single clearest way to find out, before you sign anything, which side of this you are on.
Who Actually Owes It
The charge follows the person who owned the land at the moment its use changed, not necessarily the person who ends up living there. The state's own worksheet gives the example directly: a developer who begins building a house in March owes the conversion charge even if the house sells in September. The buyer who closes on a finished new build is not automatically off the hook either, since an unpaid charge becomes a special assessment on the next property tax bill tied to the parcel, regardless of who currently holds title.
That makes it worth asking a direct question before closing on any recently split parcel or new construction near Spring Green: has the conversion charge already been assessed and paid, or is it still pending against this land. If nobody can answer that clearly, it is worth a call to the county treasurer's office for whichever county the parcel sits in before earnest money changes hands.
Before You Write An Offer On Ag-Adjacent Land
A few steps, in order, before a buyer gets attached to a specific parcel near Spring Green:
- Ask the seller for the current agricultural classification on the parcel and whether any portion has already been converted.
- Request the statutory use-value notice in writing rather than taking a verbal answer at face value.
- Estimate which acreage tier the intended homesite falls into, since fewer than 10 acres carries the highest rate.
- Confirm which county actually holds the parcel. For land inside or near the village, that is the Sauk County Land Resources & Environment Department, where a Certified Survey Map is required for minor land divisions and the CSM submittal process runs through the county's OpenGov portal. Parcels further out toward Iowa or Richland counties fall under a different planning department entirely.
- Build the estimated conversion charge into total acquisition cost as its own line item, separate from the purchase price.
The Ground Itself Still Matters
None of this changes why people want land near Spring Green in the first place. The village sits along the Lower Wisconsin State Riverway, and just up the road, the Wintergreen Nature Preserve, a 245-acre property near Taliesin now under permanent conservation protection, is a reminder of how much of this landscape is shaped by decisions about what land is allowed to become. A buyer's own decision about a five-acre homesite is smaller in scale but runs on the same logic. What a parcel is classified as today determines what it costs to change tomorrow.
FAQ
Does the conversion charge apply if the land I'm buying is already classified residential? No. The charge only applies when land currently assessed as agricultural changes to a non-agricultural use. Land already on the roll as residential, undeveloped, or forest is not subject to it.
Can I avoid the charge by keeping part of the parcel in agricultural use? Possibly, for the portion that stays in production. The charge is based on the acreage that actually changes use, so a homesite carved from a larger working farm may only trigger the charge on the converted portion, not the whole parcel, though the specifics depend on how the assessor classifies the remaining acreage.
Does this apply to land inside the Village of Spring Green or just the surrounding township? The conversion charge is a state law tied to how the local assessor has classified a parcel, not to municipal boundaries. Land inside the village limits that is still on the roll as agricultural is treated the same as township land under the same statute.
If you are looking at land near Spring Green and want a second set of eyes on what a specific parcel's assessment history actually says before you write an offer, Beth Baty has spent more than three decades in property management and real estate across Dane County and the surrounding Wisconsin communities. Let's Connect and walk through what a given piece of ground is really going to cost once the paperwork catches up with the price tag.
