This paper reports information on size and growth of snakes in two populations of Lampropeltis nigra (Black Kingsnake) over 20 years of study and provides a comparative analysis that builds on the work of Jenkins et al. (2001). During a 7-year study (1990–1996) at the Anderson County Wildlife Sanctuary (ACWS) and a 13-year study (1997–2009) at the University of Tennessee Forestry Resources Research and Education Center (FES) in Oak Ridge, TN, we captured 265 individual Black Kingsnakes a total of 556 times. The size of Black Kingsnakes in these two populations are the smallest reported for this species, with mean (± SD) snout-to-vent length (SVL) of 66.9 ± 24.5 cm (maximum = 112 cm) at ACWS and 55.8 ± 16.8 cm (maximum = 87 cm) at FES. At FES, the mass-SVL relationship is represented by an exponential equation (mass [g] = 0.0004 SVL [cm]-^2,98) similar to ACWS (mass [g] = 0.0005 SVL [cm]^2,95). Across both sites, juvenile kingsnakes grew 1.1 cm/mo faster than adult individuals. There was a significant decline in body condition index (BCI) in the combined population during 1990–2009, with BCI declining by 0.960 units annually at ACWS and by 0.981 units annually at FES over the respective study periods. Declines in BCI may be a precursor to a decline in abundance.