Our aim was to identify polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzo-p-furans (PCDFs) in agricultural farmland soils in the Northwest of Mexico. We obtained ≈50 g of soil in five Yaqui Valley (VY) agricultural fields in the north-western Mexican State of Sonora and in five Culiacán Valley (VC) agricultural fields in the north-western Mexican State of Sinaloa. Fields with minimal tillage, with ferti-irrigation, and those with intensive aerial and manual tillage were included. All soil samples were subjected to the chemical activated luciferase gene expression (CALUX(®)) test to determine PCDD/F. On average, samples contained 4.2 ± 1.2 PCDD/F ppt TEQ; VY soil samples contained 4.72 ± 1.23 PCDD/F ppt TEQ, while VC soil samples showed 3.6 ± 1.1 PCDD/F ppt TEQ (p = 0.47). On considering tillage-type, in agricultural fields catalogued as intensive tillage, PCDD/F concentrations were 4.40 ± 0.43 in agricultural fields catalogued as intensive tillage, while in farmlands of another tillage-type these concentrations were slightly higher (5.53 ± 0.8).