Human decompositional changes and the post-mortem interval (PMI) required to produce those effects have been demonstrated to vary tremendously based on environmental conditions specific to the region in which decomposition is taking place. Studies to that effect have been conducted in select areas throughout the country, but have yet to be undertaken in southeastern Pennsylvania, New Jersey, and Delaware. Given the hypothesis regarding regional differences in the rate of decay, this study set out to assess the decomposition process as it applies to the Delaware River Valley (DRV) region and to provide formulas from which to estimate time since death. The dearth of studies in this area, highlighted the need for region-specific standards, increased the accuracy of time since death estimates, and improved quantitative methods. To this end, a retroactive approach was taken in which cases from the Delaware Office of the Chief Medical Examiner with a known "date last seen" and "date recovered" were compiled. Using these cases, a qualitative analysis was conducted examining the specific decompositional changes which occur in various contexts. Quantitatively, a linear regression analysis was employed to determine if accumulated degree days (ADD) or PMI explained more of the variation in decomposition. To complement this work, a multivariate regression analysis was conducted to identify key covariates and assess their impact on the rate of decay. Lastly, to validate region-specific standards, the DRV models were compared to those presented in Megyesi et al. (2005). For this validation process, a specific progression to decomposition in the DRV was identified and total body score (TBS) systems for both outdoor and indoor cases, and aquatic depositions, were developed. ADD and TBS were determined to be central components in modeling decay. In addition, outdoor cases were demonstrated to decompose fastest. Finally, the DRV model explained more of the variation in decomposition and more accurately estimated ADD than that of Megyesi et al. (2005). In total, a set of time since death estimation formulas applicable to indoor, outdoor, and aquatic contexts were produced, and region-specific standards best-suited to estimating time since death in the Delaware River Valley were developed.