A Field That Grew Corn Last Year Probably Holds Beans This Fall

A crop map from the previous year usually names something different from what grows there this fall. Looking across Illinois's 102 counties, we found that corn or soybeans stayed unchanged on just 17.1 percent of acres between consecutive years. In six guesses based on the previous label, about five would be wrong. Going back two years gives a much better match. Harvest timing then determines whether that crop remains in the field.

Each winter, NASS releases its Cropland Data Layer (CDL). The release date for the 2025 map was February 27, 2026. Our analysis used Illinois maps spanning 2015 through 2025. We selected each 30 meter pixel classified as corn or soybeans, then checked its classification in the following year. With 0.222 acre covered by each pixel, pixel percentages also describe percentages of mapped area. Throughout this article, we refer to that area as acres.

A corn classification repeated on 21.0 percent of acres. For soybeans, the repeat share was 12.7 percent. All remaining acres received a different label. Soybeans replaced corn on 75.9 percent, and corn replaced soybeans on 81.5 percent. A few percentage points shifted into wheat, hay, pasture or land outside cropland. Across both starting crops, unchanged labels accounted for 17.1 percent of acres; changed labels accounted for 82.9 percent. Among the eight pairs of consecutive years, repeat shares ranged between 13.2 and 20.9 percent. None approached half.

Classification mistakes could account for part of the switching, so we checked that possibility. According to NASS's Illinois accuracy assessment for 2023, corn classifications were correct at 96.6 percent, with soybeans at 96.0 percent. That allows a few percentage points of error, far short of explaining a change of 75.9 percent. We repeated the analysis using only pixels surrounded by matching labels in a 3 by 3 block. This avoids field boundaries, where classifications can blend together. Those interior pixels repeated at 14.9 percent, below the full-pixel result of 17.1 percent.

County repeat shares span an eightfold difference. The chart groups counties according to those shares.

More cropland generally goes with less repetition. Among the 20 counties holding the largest corn and soybean areas, the median repeat share was 12.7 percent. For the 20 holding the smallest areas, it was 30.6 percent. All eight counties at the low end fall within east-central Illinois, at latitudes between 39.5 and 40.9 degrees north. Their repeat shares range between 7.3 and 8.1 percent. Douglas, Coles, De Witt, Edgar, McLean and Piatt head that group. Rates below 20 percent occur in 62 counties out of 102. Five counties exceed 45 percent. Four of those are Hardin, Johnson, Union and Alexander, where the highest share reaches 60.7 percent. Those counties also belong to the nine with the smallest corn and soybean areas, leaving relatively few pixels behind their rates. Carroll's repeat share is 50.8 percent, and its area ranks 50th when counted upward from the smallest.

We tested a simple crop swap by setting aside the final year. Earlier maps supplied predictions for 2024 in three counties whose repeat shares differed sharply.

Predicting soybeans after corn and corn after soybeans matched 93.0 percent of acres in McLean, 78.5 percent in Pike and 59.5 percent in Jo Daviess. Another rule examined each pixel's crop history. It predicted an unchanged crop only for pixels that seldom switched. Compared with the simple swap, that approach improved accuracy by 0.4, 3.0 and 12.2 points, respectively. It also won every comparison across the 9 county-year tests. The checks compare predicted pixel classifications with map classifications; they do not use farm records. For McLean, swapping crops gets almost all the way there. Past classifications contribute more in Jo Daviess, although the history-based rule still got 28.3 percent of acres wrong.

This rotation pattern also determines how useful an aging crop map can be.

Looking back one year yields matching crop labels on 17.1 percent of pixels. At a two-year gap, agreement rises to 79.4 percent. With three years between maps, it falls to 25.7 percent; with four, it returns to 73.3 percent. Alternation dominates the mapped acres classified as corn or soybeans. An even number of years therefore usually returns to the original crop, while an odd number usually points to the opposite crop. Where a three-year-old map identifies beans, corn now occupies 72.2 percent of those pixels.

Adding up the state conceals these exchanges.

During every year spanning 2016 to 2025, corn occupied 28.8 to 31.8 percent of mapped Illinois area. Soybeans occupied 26.6 to 29.0 percent. Those statewide shares stayed within their ranges as individual acres switched crops. Our county crop table records similarly steady shares for the other five states in our holdings. Across 2020 to 2024, each state's average county share for corn or soybeans changed by no more than 3.0 points in Iowa, Kansas, Missouri, Ohio and Wisconsin, along with Illinois. Individual counties could change more. A county crop chart can therefore appear correct even when a particular field is labeled with the wrong crop.

Knowing the crop resolves only part of the question. You also need to know whether harvest has reached that field. Under NASS's definitions for Crop Progress, harvest means the crop has been cut, threshed or gathered from the field by another means. People reporting conditions, primarily extension agents and Farm Service Agency employees, supply estimates reflecting conditions on Sunday.

For the average covering 2019 to 2023, corn harvest in Illinois led soybean harvest throughout September. By September 29, harvested shares reached 16 percent for corn and 11 percent for soybeans. The lead changed during October's second week. On October 13, harvest had reached 44 percent for corn versus 47 percent for soybeans. Beans subsequently pulled ahead by up to 8 points. As of November 10, soybean harvest reached 93 percent, compared with corn's 89 percent. The unfinished acres are what matter here. On November 10, corn remained unharvested on 11 out of every 100 acres, while soybeans remained unharvested on 7 out of every 100 acres.

Early this fall, harvest progress was ahead of average. In the report dated September 28, 2026, Illinois's harvested shares were 26 percent for corn and 21 percent for soybeans as of September 27. The corresponding averages for 2021 to 2025 were 17 and 14. Our standing corn guide explains how an uncut block affects a hunt. Here, the purpose is simply to estimate whether that block remains.

We measured crop transitions in Illinois alone. We have no measurements of those transitions for other states. The layer uses satellite-based crop classifications, and NASS cautions that no farmer-reported data can be derived from it. Beginning in 2024, NASS mapping uses 10 meters; the copies we analyzed use a 30 meter grid. For that reason, our main result draws on the eight consecutive-year pairs spanning 2015 through 2023. Results for the two pairs involving 2024 and 2025 were 14.2 and 15.0 percent, respectively, within the same range.

County averages combine farms that can differ greatly. An individual field may break the pattern. Our prediction test includes three counties. Crop Progress percentages apply statewide and cannot describe a particular county or field. We drew the averages covering 2019 to 2023 from reports NASS issued in 2024. Those averages will change as additional years are included.

First, determine how old the image is. Work out how many years separate this fall from the aerial or crop map. Our probabilities were calculated from crop maps, but the same reasoning fits an aerial when you can identify its crop. Odd gaps, including a map from last year or an aerial taken three years ago, usually suggest soybeans if the older view showed corn, or corn if it showed soybeans. Even gaps usually point to a repeat. After that, check past crops for the field. On NASS's map of Crop Sequence Boundaries, you can interact with estimated field outlines and view crop histories spanning 2018 to 2025. Consistent annual alternation gives the clearest case. In our prediction test, using crop history outperformed simple swapping across all 9 county-year comparisons.

Then use the state's harvest share as a broad starting estimate. A Crop Progress figure showing Illinois soybean harvest at 47 percent means roughly half of soybean acreage statewide has been cut. An unseen field could belong to either group. The percentage covers the state rather than that particular field. Finish with a direct check: drive along its edge or ask the operator about the combine's arrival. Avoid basing your hunting plan on an inferred crop alone. Before relying on images, establish their dates with our two-date imagery guide.

Every field has four separate clocks. Each resolves a different question.