The arrangement of ionic liquids (ILs) within mesoporous ordered silica SBA-15 is revealed from nitrogen physisorption experiments combined with non-local density functional theory analysis of the pore structure and mean-field density functional theory (MFDFT). Using MFDFT on simple lattice models, we outline possible scenarios for IL distributions within the pores and conditions under which they originate. MFDFT predictions for nitrogen adsorption on these models of pore structures modified with ILs are in qualitative agreement with the experimental results. They demonstrate that the distribution of the ILs inside the pores of SBA-15 is sensitive to solid-fluid interactions, leading to different structures as a function of loading. This study also recommends the MFDFT and lattice models as a powerful framework for the interpretation of nitrogen sorption behavior, which complements the existing theoretical and experimental techniques to characterize the structure of supported ILs.