Twelve Northeastern US herds were enrolled in a prospective cohort study with the objective of identifying associations of early lactation rumen-protected Met supplementation with herd level health, production performance, and management. Farms were enrolled as either experiment (EXP; n = 7 herds; feeding >11.25 g/d of rumen-protected Met postpartum; Smartamine M; Adisseo, Antony, France) or control (CON; n = 5 herds; postpartum diet containing ≤11.25 g/d of supplemental Met). Data were analyzed in SAS v. 9.4 using the MIXED, MEANS, and FREQ procedures, and means ± SD are reported throughout. In the formulated postpartum diet, EXP herds had higher levels of Met (1.04 ± 0.03 vs. 0.94 ± 0.05 g Met/Mcal ME; P < 0.01 and 2.52 ± 0.06 vs. 2.32 ± 0.11 Met as % MP; P < 0.01). Postpartum pooled plasma Met concentrations (12 to 15 cows/herd) were greater in EXP herds compared with CON (4.05 ± 0.50 vs. 3.32 ± 0.13 μg/mL; P = 0.01). Compared with CON, EXP had greater average milk yield at 4 wk postpartum (WK4M; 48.8 ± 1.4 vs. 43.4 ± 4.5 kg; P = 0.02), combined fat and protein yield (2.81 ± 0.15 vs. 2.47 ± 0.26 kg; P = 0.04) and 305-d mature equivalent milk (13,473 ± 349 vs. 12,122 ± 413 kg; P = 0.03). Female calf dead on arrival rate (DOA) was lower in EXP compared with CON (4.6 ± 1.1 vs. 8.8 ± 2.5%; P < 0.01), and EXP herds had a numerically lower 60 d cull rate than CON (8.8 ± 4.4 vs. 11.5 ± 5.3%; P = 0.37). Postpartum feed pushup frequency was greater for EXP herds than CON (86% vs. 0% pushup ≥ 6x/d; P = 0.03; n = 10). After standardizing ingredient cost and milk price, diet cost estimates based on WK4M tended to be lower for EXP (5.03 ± 0.38 vs. 5.76 ± 0.87 $/45.4 kg of milk; P = 0.09). Overall, postpartum supplementation with rumen-protected Met was associated with higher levels of plasma Met, greater 305-d mature equivalent milk yield, WK4M, and combined fat and protein yield at the herd level.