The objective of this study was to characterize the genetic relationship of production traits in US organic Holstein cows during the grazing and non-grazing season. Eleven US organic dairy herds provided 18,894 testday milk yield records and up to 11,435 testday component records from 3,654 and 2,201 cows, respectively, during the grazing season (May through August) and 16,222 testday milk yield records and up to 11,373 testday component records from 3,117 and 2,386 cows, respectively, from December through March (non-grazing season). Means within the grazing season were 28.27 kg/d, 3.66%, 3.00%, 0.93 kg/d, and 0.76 kg/d for milk yield, fat %, protein %, fat yield, and protein yield, respectively. Means during the non-grazing season were 28.14 kg/d, 3.90%, 3.16%, 1.02 kg/d, and 0.83 kg/d for milk yield, fat %, protein %, fat yield, and protein yield, respectively. Variance components within and genetic correlations between the 2 seasons were established using repeated records, treating each season as a separate trait in 2-trait animal models. Fixed class effects of age group at parturition within lactation group, year of parturition within herd, and days in milk group within lactation group were included in all models along with random effects of testday within herd, animal, and permanent environment. The pedigree consisted of 22,900 animals. For all traits, residual variances were generally greater during the grazing season whereas additive genetic variances were greater in the non-grazing season. Parameter estimates for fat % displayed the largest difference between grazing and non-grazing seasons, respectively, for additive genetic variance (0.09 ± 0.014 and 0.13 ± 0.019), heritability (0.20 ± 0.02 and 0.30 ± 0.03) and repeatability (0.27 ± 0.01 and 0.43 ± 0.01). Genetic correlations between grazing and non-grazing seasons were 0.93 ± 0.05, 0.90 ± 0.04, 0.93 ± 0.04, 0.96 ± 0.05, 0.96 ± 0.04, for milk yield, fat %, protein %, fat yield, and protein yield, respectively. In conclusion, fat percent appears to be most influenced by season, though overall, the strong genetic correlations between grazing and non-grazing seasons suggest that the genetic basis of production does not strongly change in association with the grazing season.