Extensive density functional theory (DFT) calculations are carried out on various structural isomers of protonated methanol clusters, H⁺(MeOH)_n (n = 2-9), to analyze the morphological development of the hydrogen bond network in the clusters with an increase of the cluster size. Coexistence of multiple structural isomers is demonstrated by the nearly degenerated energies. Moreover, significant temperature dependence of the preferential isomer structure is shown by the calculated Gibbs free energies. The previously reported infrared spectra of H⁺(MeOH)_n (J. Phys. Chem. A 2005, 109, 138) are revisited on the basis of the spectral simulations of the isomers by DFT calculations.