This thesis demonstrates that a parameter-free density functional theory that includes ion-ion correlations and ion-solvent interactions is in agreement with the data over the entire range of experimentally tunable correlation coupling strengths. The reported findings represent a significant advance towards understanding the nature and role of ion correlations in charged soft-matter. Ion distributions underlie many scientific phenomena and technological applications, including electrostatic interactions between charged biomolecules and the efficiency of energy storage devices. These distributions are determined by interactions dictated by the chemical properties of the ions and their environment, as well as the long-range nature of the electrostatic force. The presence of strong correlations between ions is responsible for counterintuitive effects such as like-charge attraction.