This is a tab-delimited text file. The file contains nesting date and mean temperatures for each day of the thermosensitive period for sex determination (TSP, July) in 16 natural painted turtle (Chrysemys picta) nests. Each of these nests resulted in the production of both male and female offspring (i.e. mixed-sex nests). Temperature data were collected using thermal data loggers within the nests and these means were derived from hourly temperature trends. The data were collected from nests at the Thomson Causeway Recreation Area in Thomson, IL. These data were used to estimate the historic slope of temperature change over the entire TSP. A key to the column labels is in the READ ME file.