Nitrapyrin is a nitrification inhibitor that is co-applied with N-fertilizer in agroecosystems. Over the course of one year (March 2016 to June 2017), 192 water samples from seven streams across Iowa and Illinois were analyzed for nitrapyrin, its degradate 6-chloropicolinic acid (6-CPA), and three widely used herbicides acetochlor, atrazine, and metolachlor. Additional environmental samples were collected and analyzed in spring 2017: 63 water samples from eight subsurface drains, and 33 soil samples from a field in Iowa that received direct application of nitrapyrin (only for nitrapyrin and herbicides). Nitrapyrin was detected in all seven streams (56% detection) with concentrations ranging from 4 to 1,200 ng/L; 6-CPA was detected in six of the seven streams (13% detection) with concentrations ranging from 2 to 13 ng/L. Nitrapyrin was detected in only two of the eight subsurface drains and in 10% of drain samples (10% detection), and with concentrations ranginged from 3 to 12 ng/L; 6-CPA was detected in six of the eight subsurface drains and in (33% of drain samples withdetection), and concentrations ranginged from 2 to 6 ng/L. Nitrapyrin was detected in 67% of the soil samples collected, and concentrations ranged from 0.9 to 42 ng/g. Generally, all three herbicides were detected more frequently and at higher concentrations than nitrapyrin in the streams, subsurface drains, and soils. There are 3 csv datasets related to this data release. Please find in each of the child items the data and metadata.