An ionic liquid (IL) based dispersive liquid–liquid microextraction combined with HPLC hydride generation atomic fluorescence spectrometry method for the preconcentration and determination of mercury species in environmental water samples is described. Four mercury species (MeHg+, EtHg+, PhHg+, and Hg2+) were complexed with dithionate and the neutral chelates were extracted into IL drops using dispersive liquid–liquid microextraction. Variables affecting the formation and extraction of mercury dithizonates were optimized. The optimum conditions found were as follows: IL-type and amount, 0.05 g of 1-octyl-3-methylimidazolium hexafluorophosphate; dispersive solvents type and amount, 500 μL of acetone; pH, 6; extraction time, 2 min; centrifugation time, 12 min; and no sodium chloride addition. Under the optimized conditions, the detection limits of the analytes were 0.031 μg/L for Hg2+, 0.016 μg/L for MeHg+, 0.024 μg/L for EtHg+, and 0.092 μg/L for PhHg+, respectively. The repeatability of the method, expressed as RSD, was between 1.4 and 5.2% (n = 10), and the average recoveries for spiked test were 96.9% for Hg2+, 90.9% for MeHg+, 90.5% for EtHg+, 92.3% for PhHg+, respectively. The developed method was successfully applied for the speciation of mercury in environmental water samples.