The room-temperature thermodynamic and structural properties of acetonitrile clusters containing alkali ions (Na+, Cs+) or halide ions (I-) are investigated via Monte Carlo simulations. An intermolecular potential function including Coulombic, polarization, and repulsion-dispersion terms was parameterized on the basis of high-level CCSD(T)/6-311+G(2df,pd)//MP2/6-311+G(d) ab initio calculations, supplemented by experimental data for molecular and ionic polarizabilities. Cluster thermodynamic properties such as binding enthalpies evaluated from the Monte Carlo simulations are in good agreement with available experimental data, which inspires confidence in the simulation results. These properties are shown to converge very slowly to their bulk limit, in agreement with earlier predictions of the liquid drop model, and their evolution with cluster size is closely related to the solvation structure of the ionic clusters. All Na+(CH3CN)(n), Cs+(CH3CN)(n), and I-(CH3CN)(n) clusters exhibit an interior solvation structure. However, if the Na+(CH3CN)(n) and Cs+(CH3CN)(n) room-temperature radial probability distributions exhibit very distinct, sharp peaks, those for large I-(CH3CN)(n) clusters are broader, because of much weaker iodide-solvent interactions. The solvent coordination numbers for the first solvation shell are ca. 6, 7, and 9 for Na+(CH3CN)(n), Cs+(CH3CN)(n), and I-(CH3CN)(n), clusters, respectively. The completion of the ion first solvation shell is accompanied by a significant decrease of the stepwise binding enthalpies, a finding that is more pronounced for cationic clusters. Finally, comparison with previous results for ion-water clusters demonstrated the importance of the relative strengths of ion-solvent and solvent-solvent interactions in the determination of interior vs surface ionic cluster structures. For example, I-(CH3CN)(n) clusters clearly exhibit an interior solvation structure, in net contrast with the surface structures observed for I-(H2O)(n) clusters.