The term "ionic liquid" in the general sense was used as early as 1943.
The discovery date of the "first" ionic liquid is disputed, along with the identity of its discoverer. Ethanolammonium nitrate (m.p. 52–55 °C) was reported in 1888 by S. Gabriel and J. Weiner. In 1911 Ray and Rakshit, during preparation of the nitrite salts of ethylamine, dimethylamine, and trimethylamine observed that the reaction between ethylamine hydrochloride and silver nitrate yielded an unstable Ethylammonium nitrite ()· , a heavy yellow liquid which on immersion in a mixture of salt and ice could not be solidified and was probably the first report of room temperature ionic liquid. Later  in 1914, Paul Walden reported one of the first stable room temperature ionic liquids ethylammonium nitrate ()· (m.p. 12 °C). In the 1970s and 1980s, ionic liquids based on alkyl-substituted imidazolium and pyridinium cations, with halide or tetrahalogenoaluminate anions, were developed as potential electrolytes in batteries.
For the imidazolium halogenoaluminate salts, their physical properties&mdash;such as viscosity, melting point, and acidity&mdash;could be adjusted by changing the alkyl substituents and the imidazolium/pyridinium and halide/halogenoaluminate ratios. Two major drawbacks for some applications were moisture sensitivity and acidity or basicity. In 1992, Wilkes and Zawarotko obtained ionic liquids with neutral weakly coordinating anions such as hexafluorophosphate () and tetrafluoroborate (), allowing a much wider range of applications.