Abstract The aim of this study was to characterize the American Angus cattle population in terms of changes to the inbreeding rate (ΔF) and effective population size (Ne) before and after the implementation of genomic selection (GS). Genomic information (89,206 SNPs) was obtained for 25,960 bulls and 134,962 cows born between the years 2000 and 2017. Bulls and cows were independently grouped into two groups based on year of birth, pre-GS (2000–2009), and post-GS (2010–2017). Genomic inbreeding (FGRM) was calculated assuming fixed allele frequencies (0.5). Inbreeding based on runs of homozygosity (FROH) was calculated using software SNP1101 (Sargolzaei, 2014). The yearly ΔF for each group was estimated by regressing the inbreeding coefficients on year of birth. The generation intervals (L) were calculated for each of the four pathways of selection at both time periods (pre-GS and post-GS), where the mean of the sires of sires and dams of sires pathways was taken to be the generation interval for the bulls and the mean of the sires of dams and dams of dams pathways was taken to be the generation interval for the cows. The L and ΔF of the three inbreeding coefficients were used to estimate the Ne. Estimates of ΔF and Ne for both sexes at the two time periods can be found in table 1. In both sexes, ΔFROH decreased and NeROH increased from pre-GS to post-GS. For bulls, ΔFGRM and NeGRM did not change, and for cows, ΔFGRM decreased and NeGRM increased from pre-GS to post-GS. These results suggest that the implementation of genomic selection in Angus cattle has not caused the increased inbreeding rates and reduced effective population sizes seen in other species, but instead has been beneficial for the preservation of genetic diversity.