Understanding the kinetics and thermodynamics of the stabilizing interactions in non-coding RNA provides crucial information about their structural dynamics and ultimately, their biological function. The use of single-molecule FRET methods allows us to investigate the real-time folding and unfolding of an isolated GAAA tetraloop-receptor interaction in the Tetrahymena ribozyme. Cation-dependent folding studies of this ubiquitous interaction show that increasing concentrations of Na+ significantly increase the rate constant for docking and slightly decrease the rate constant for undocking. We examine the temperature-dependence of this Na+-induced folding in order to determine the thermodynamic parameters associated with the folding and unfolding processes. At 150 mM Na+ the folding process is exothermic (ΔH° = −20 kcal/mol) but with a significant entropic cost (ΔS° = −67 cal/mol K), leading to a near zero ΔG° at 298 K. Increasing concentrations of Na+ dramatically increase both ΔH° and ΔS°, with the competition yielding a decrease in ΔG°. For example, by 600 mM Na+ the folding process even becomes endothermic (ΔH° = 4.3 kcal/mol) and entropically rewarding (ΔS° = 20 cal/mol K), with the folding process now becoming slightly favorable (ΔG° = −1.7 kcal/mol). These results indicate that increasing Na+ concentration favors folding by increasing entropic gains more than enthalpic losses, which leads to a more favorable folding free energy change. We propose a model that uses the competing roles of solvent and structure to explain these gains and losses.