README: It must be emphasized that any pixel count or acreage data derived from these CDL county spreadsheets or through the CroplandCROS website are not considered official NASS acreage estimates. There will be differences between raw pixel count summaries of the CDL and official NASS estimates when comparing acreage statistics at the state, district, and county levels. Statistics generated by CroplandCROS and represented in these county spreadsheets are dependent upon pixel counting. Pixel counting is usually downward biased when compared to the official estimates. Counting pixels and multiplying by the area of each pixel will result in biased area estimates and should be considered raw numbers needing bias correction. Official crop acreage estimates at the state and county level are available at https://www.nass.usda.gov/.
Here are three references discussing the subject matter of pixel counting and estimation:
 a) Gallego F.J., 2004, Remote sensing and land cover area estimation. International Journal of Remote Sensing. Vol. 25, n. 15, pp. 3019-3047.
 b) European Commission, Joint Research Centre, MARS;  Best practices for crop area estimation with Remote Sensing - Section 4.1.1.
 c) Czaplewski, R. L. (1992). Misclassification bias in areal estimates. Photogrammetric Engineering and Remote Sensing, 58, 189-192.

There are several grouped categories that have been tabulated, such as Soybeans_all which includes all soybean-related crop categories. Below are the category groupings:
    Corn_all         = Category_001 + Category_225 + Category_226 + Category_228 + Category_237 + Category_241;
    Cotton_all       = Category_002 + Category_232 + Category_238 + Category_239;
    Sorghum_all      = Category_004 + Category_234 + Category_235 + Category_236;
    Soybeans_all     = Category_005 + Category_026 + Category_239 + Category_240 + Category_241 + Category_254;
    Barley_all       = Category_021 + Category_233 + Category_235 + Category_237 + Category_254;
    Wheat_Durum_all  = Category_022 + Category_230 + Category_234;
    Wheat_Winter_all = Category_024 + Category_026 + Category_225 + Category_236 + Category_238;
    Oats_all         = Category_028 + Category_226 + Category_240;
    Canteloupe_all   = Category_209 + Category_231;
    Lettuce_all      = Category_227 + Category_230 + Category_231 + Category_232 + Category_233;

Technical questions can be directed to the NASS Spatial Analysis Research Section (SARS) at SM.NASS.RDD.GIB@usda.gov