Alopecurus myosuroides (blackgrass) is a problematic weed of Western European winter wheat and its success is largely due to widespread multiple-herbicide resistance. Previous analysis of F2 seed families derived from two distinct blackgrass populations exhibiting equivalent non-target site resistance (NTSR) phenotypes shows resistance is polygenic and evolves from standing genetic variation. Using a CIDER-seq pipeline we show that herbicide resistant (HR) and herbicide sensitive (HS) F3 plants from these F2 seed families as well as the parent populations they were derived from carry extra-chromosomal circular DNA (eccDNA). We identify the similarities and differences in the coding structures within and between resistant and sensitive populations. Although the numbers and size of detected eccDNAs varied between the populations, comparisons between HR and HS blackgrass populations identified shared and unique coding content, predicted genes, and functional protein domains. These include genes related to herbicide detoxification such as Cytochrome P450s, ATP-binding cassette transporters and glutathione transferases including AmGSTF1. eccDNA content was mapped to the Alopecurus myosuroides reference genome, revealing genomic regions at distal end of chromosome 5 and the near center of chromosome 1 and 7 as regions with high number of mapped eccDNA gene density. Mapping to 15 known herbicide-resistant QTL regions showed the eccDNA coding sequences match 12 with four QLT matching HS coding sequences one region only contained HR coding sequences. These findings establish that like other pernicious weeds, blackgrass has eccDNAs that contain homologs of chromosomal genes, and these may contribute genetic heterogeneity and evolutionary innovation to rapidly adapt to abiotic stresses including herbicide treatment.