Previous experimental studies [Sliwinska-Bartkowiak et al., Chem. Phys. Lett. 1983, 94, 609] indicate that o-nitrotoluene/n-decane and m-nitrotoluene/n-decane mixtures are of particular interest because they exhibit anomalous behavior in the nonlinear dielectric effect near the upper critical solution point, and it has been surmised that these effects are due to an increase in cluster formation as each mixture approaches its critical point. In this work, Monte Carlo simulations are performed using the TraPPE force field at multiple temperatures, concentrations, and electric field strengths to examine the structural microheterogeneity of these mixtures and determine the dielectric constants and nonlinear dielectric effect. At low field strength, the simulations indicate substantial structural microheterogeneities, but these persist over a wide range of conditions. At high field strength (an order of magnitude higher than in the experimental work), the simulations indicate a field-induced segregation.