Ketosis is a common metabolic disease in postpartum dairy cows due to negative energy balance at the onset of lactation resulting from low dry matter intake and disorders of energy metabolism. Ketosis results in hyperketonemia, hypoglycemia, decreased milk yield, and is often associated with other primary health disorders. To estimate the incidence of subclinical (SCK) and clinical ketosis (CK) in the California Central Valley, blood samples and milk production data were collected from 10 commercial dairy herds in Tulare, Kings, and Kern counties. In February 2018, an average of 17 multiparous Holstein cows from each herd were bled during wk 1 and wk 2 postpartum and whole blood was analyzed for glucose and acetoacetate (AcAc) levels using NovaMax meters (Nova Diabetes Care, Inc., Billerica, MA). Ketosis was defined as SCK at 1.0–1.4 mmol/L and CK > 1.4 mmol/L AcAc in whole blood. Previous lactation milk fat yield and 305-d equivalent milk yield were collected from DairyComp305 (Valley Ag Software, Tulare, CA). All data were analyzed using the Mixed Procedure of SAS with repeated measures by cow or a Generalized Linear Model Procedure (v. 9.4, SAS Institute 2015). Across all herds, average SCK was 12% (repeat cases 5%) and CK was 11% (repeat 61%). All repeat CK cases progressed from SCK in wk 1. Across herds, the lowest incidence of hyperketonemia (>1.0 mmol/L AcAc) was 0% and the highest incidence was 44%. Glucose and AcAc were inversely related (P < 0.001; R² = 0.12). Hyperketonemic cows produced 393 kg more milk (P = 0.1) and 44 kg more milk fat (P = 0.02) in their previous lactation compared with non-ketotic cows. Five dairies housed fresh cows in free stall corrals and 5 dairies housed fresh cows in free stall corrals with an attached exercise corral or in an open lot style corral. Cows with access to an exercise corral or housed in an open lot had lower blood AcAc levels compared with cows housed in free stalls (0.55 vs. 0.64 mmol/L; P = 0.02, R² = 0.17) and had a decreased recurrence of a ketotic event in the same lactation (5% vs. 26%). Therefore, factors affecting blood AcAc levels on these commercial herds were glucose, previous lactation milk and fat yield, and access to an exercise corral.