The current resistance status of mosquitos to common insecticides raises the concern for innovative formulations with novel active ingredients, especially for those who can transmit pathogens. In addition to being effective, these are not allowed to harm the environment and non-target organisms. In this context, some imidazolium salts are promising candidates due to their excellent larvicidal action against Aedes aegypti, however, the understanding of their impact on environment and non-target organisms is limited. Herein, the toxicity of two imidazolium salts (1-methyl-3-octadecylimidazolium chloride (C₁₈MImCl) and 1-hexadecyl-3-methylimidazolium methanesulfonate (C₁₆MImMeS)) were tested in Culex quinquefasciatus larvae and their (cyto)toxic potential in Lactuca sativa seeds, mouse lung fibroblasts, human keratinocytes and Wistar rats. C₁₆MImMeS showed excellent larvicidal activity (LC₅₀: 24 h: 5.751 µg/mL; 48 h: 4.613 µg/mL), but negatively influenced the Lactuca sativa germination rate and size of radicles and hypocotyls, together with other phytotoxic characteristics. C₁₈MImCl also showed being a potent larvicidal (LC₅₀: 24 h: 3.848 µg/mL; 48 h: 3.175 µg/mL), without presenting phytotoxicity against Lactuca sativa. C₁₆MImMeS was more cytotoxic to mouse lung fibroblast and human keratinocyte cells than C₁₈MImCl. Besides, the lethal median toxicity of 309 mg/kg of C₁₈MImCl for oral application in Wistar rats suggests its safe application in related non-target organisms. Altogether, this is the first work showing the larvicidal potential of these IS against Culex quinquefasciatus, including phytotoxicity and (cyto)toxicity data that are important for their release in mosquito controlling formulations.