As one of the prime candidates to achieve green processing of celluloses, ionic liquids (ILs) attract great attention. In this study, 9 non-reactive and reactive 1,3,4-trisubstituted 1,2,3-triazolium ILs with varied substituted groups and counteranions were designed to explore their properties as solvents and monomers for cellulose dissolution and functionalization. The nature of counteranions determined their thermal stability and cellulose solubility, but in opposite effects. Within our investigation, 1,4-dibutyl-3-methyl-1,2,3-triazolium acetate ([Bu2Tr][OAc]) IL showed the highest cellulose solubility at 15.7 wt% (40.1 g of cellulose in 1 mole of IL). The homogeneous solution was applied for subsequent cellulose functionalization reactions, while the IL solvents after reactions could be recycled with retained efficiency. A polymerizable 1,2,3-triazolium-based IL carrying a C4-vinyl group was used for the first time to prepare hybrid celluloses with grafted polytriazoliums, which showed a combination of cellulose and poly(ionic liquid)s in one polymer with enhanced interface compatibility and colloidal stability.