Uncontrolled weeds can cause billions of dollars in yield loss in corn and soybean production fields in the United States. Growers often use herbicides to control weeds to avoid yield loss. The objective of this study was to estimate the cost of herbicides used in corn and soybean production in the United States. On-farm herbicide usage data were extracted from corn (2021) and soybean (2023) surveys of the United States Department of Agriculture–National Agricultural Statistics Service (USDA-NASS 2022a, 2024a) Agricultural Chemical Use Program. Commonly used or known products were assumed for each reported herbicide. Based on the USDA-NASS surveys, approximately 107.8 and 89.1 million kg of herbicides were applied in corn and soybean production in 2021 and 2023, respectively, in the United States. Glyphosate (33.8 million kg; in various salt forms), atrazine (26.8 million kg), and mesotrione (2.4 million kg) were the most widely applied herbicides, on 79%, 65%, and 47% of corn, respectively, planted in 2021 (USDA-NASS 2022b). Similarly, glyphosate (in various salt forms) was the most widely applied herbicide in soybean, followed by 2,4-D (15.9 million kg; in various salt forms) and glufosinate-ammonium (4.4 million kg), which were applied to 58% and 23% of soybean, respectively, planted in 2023 (USDA-NASS 2024c). Using the average retail price of herbicide products from Kansas State University, University of Nebraska−Lincoln, and North Dakota State University publications, herbicides (excluding adjuvants and application costs) would have cost approximately $3.2 and $4.1 billion in corn and soybean in 2021 and 2023, respectively.