The liquefaction of corn cobs and switchgrass was studied using 1-(3-propylsulfonic)-3-methylimidazolium chloride and 1-(4-butylsulfonic)-3-methylimidazolium chloride Brønsted acidic ionic liquids as catalysts in acetone at 120 °C for 5 h. The highest biomass conversions to liquefied bio-oil for corn cobs and switchgrass are 63.4 ± 0.9 and 56.4 ± 0.9 % (w/w) respectively. The liquefied products were fractionated to polar and non-polar fractions by solvent extractions and analyzed using liquid chromatography - mass spectrometry (LC[sbnd]MS) and gas chromatography - mass spectrometry (GC-MS). The weights of polar fraction : non-polar fraction was 2 : 1 for all liquefied bio-oils. Sixteen products were identified from the polar fractions of liquefied bio-oils, whereas nineteen products were identified from methylene chloride soluble non-polar fractions. The compounds formed as a result of cross aldol condensations of biomass derived furans furfural and 5-hydrxymrthylfurfural with one or more acetone molecules were identified in bio-oils. Four lignin derived compounds were also found in non-polar factions of liquefied bio-oils. Corn cobs with higher hemicellulose content produced higher liquefaction product yields indicating that hemicellulose is more easily liquefied under the conditions used. The two catalysts, 1-(3-propylsulfonic)-3-methylimidazolium chloride and 1-(4-butylsulfonic)-3-methylimidazolium chloride produced practically comparable liquefaction yields, showing that structural effect of one methylene group in the catalyst is not significant.