We have studied the electrical conductivity of mixtures of the ionic liquid (IL) [C(2)mim][NTf(2)] with chloroform for various concentrations at a temperature of 303 K by both experiments and MD simulations. The molar conductivities exhibit an initial increase with decreasing IL concentration, which again sharply decreases in the region of highly diluted IL concentrations. This behavior is according to a competition between 1) the decreasing viscosity with increasing chloroform concentration due to fluidizing the mixture, and 2) the decreasing amount of charge carriers due to the formation of neutral IL aggregates. The simulated molar conductivities and their concentration dependence are found to be in reasonable agreement with the experimentally determined values, suggesting that essential correlations between the solvated ionic species in the solution are well represented. Both experiments and simulations show that the Nernst-Einstein relation drastically overestimates the conductivity of the solutions at low IL concentrations. According to our MD simulation data, this observation is due to the extensive formation of neutral aggregates in the low-concentration regime.