To understand the resistance tendencies of M. domestica populations from garbage dumps, this study conducted a survey to assist with their future management and monitoring. Samples were collected from garbage dumps in northern, central, and southern Taiwan in 2015 and 2018. Bioassay tests were conducted to study the resistance of the houseflies to 10 common insecticides: pyrethrin insecticides (cypermethrin, tetramethrin, permethrin, and deltamethrin), organophosphate insecticides (chlorpyrifos, fenitrothion and pirimiphos–methyl), propoxur, fipronil, and imidacloprid. The results revealed that houseflies’ resistance to deltamethrin has become increasingly problematic and that they have developed cross–resistance. Although fenitrothion and pirimiphos–methyl resistance had decreased, chlorpyrifos resistance had increased. In addition, although the houseflies exhibited a general trend of decreasing resistance to fipronil, their resistance to propoxur and imidacloprid increased for some strains. Overall, houseflies from garbage dumps in Taiwan have developed multiple resistance