This file contains the microsatellite genotypes for 11 loci and 904 individuals, in 29 natural populations (forest) of butternut (J cinerea L) across eastern North America. These are the data referred to in the first sentence of the Results. They are data AFTER removal of hybrid individuals, identical genotypes, or individuals with too much missing data. These data are therefore the data used to calculate all statistics in the paper. The data are in GENEPOP format. The names of individuals are unique identification numbers used in our lab. The names of the loci correspond to those from Robichaud et al, and Hoban et al, as described in the Materials and Methods of the paper.