Driven by the promising future of cellulose nanocrystals (CNCs), extensive research in the field of CNCs’ preparation has been conducted to date. This critical review provides a perspective on recent advances in the preparation of CNCs utilizing ionic liquids (ILs) as a media, from protic acidic cellulose-hydrolyzing ILs to basic ILs. The review highlights advantages and shortcomings of the synthetic methods, and describes the properties of the CNCs obtained from ILs – surface morphology, size, crystallinity, and thermal properties.