Expansive clay soils, when subjected to substantial moisture change, can be extremely problematic causing various types of damage to lightly-loaded structures. Solving these problems requires an understanding of unsaturated soil mechanics. Soil suction, related to moisture content change, is important in the development of unsaturated soil properties and in the assessment of initial and final stress for heave computation. Direct measurement of soil suction on expansive clays to determine field suction profiles is quite limited due primarily to tradition and cost-driven geotechnical field investigation practices prioritizing water content measurement over soil suction measurement. This study employs a surrogate to estimate soil suction profiles for various sites consisting of clay soils with a Plasticity Index of greater than 15. The soil suction surrogate was used to determine suction profiles from existing geotechnical engineering expansive clay field investigations and a limited amount of directly measured suction profiles were also used. Equilibrium suction magnitudes and the depths to constant suction were obtained from the field suction profiles and results were compared to data found in the existing literature. Thornthwaite Moisture Index (TMI) is a climatic index to describe climatic conditions for a given region. Surface flux boundary conditions (i.e. covered and uncovered and irrigated and non-irrigated) were investigated and comparisons were made to the extent possible. Previous studies have presented correlations between TMI and equilibrium suction and TMI and depth to constant suction. Relationships within this study are presented and comparisons are made to existing relationships. Results and recommendations for further research are discussed.