Background It is unclear what office blood pressure (BP) is the optimal treatment target range in patients with hypertension. Methods and Results Using the Korean National Health Insurance Service database, we extracted the data on 479 359 patients with hypertension with available BP measurements and no history of cardiovascular events from 2002 to 2011. The study end point was major cardiovascular events (MACE), a composite of cardiovascular death, myocardial infarction, or stroke. This cohort study evaluated the association of BP levels (<120/<70, 120–129/70–79, 130–139/80–89, 140–149/90–99, and ≥150/≥100 mm Hg) with MACE. During a median follow‐up of 9 years, 55 401 MACE were documented in our cohort. The risk of MACE was the lowest (adjusted hazard ratio [HR], 0.79; 95% CI, 0.76–0.84) at BP level of <120/<70 mm Hg, and was the highest (HR, 1.32; 95% CI, 1.29–1.36) at ≥150/≥100 mm Hg in comparison with 130 to 139/80 to 89 mm Hg. These results were consistent in all age groups and both sexes. Among patients treated with antihypertensive medication (n=237 592, 49.5%), in comparison with a BP level of 130 to 139/80 to 89 mm Hg, the risk of MACE was significantly higher in patients with elevated BP (≥140/≥90 mm Hg), but not significantly lower in patients with BP of <130/<80 mm Hg. Low BP <120/70 mm Hg was associated with increased risk of all‐cause or cardiovascular death in all age groups. Conclusions BP level is significantly correlated with the risk of MACE in all Korean patients with hypertension. However, there were no additional benefits for MACE amongst those treated for hypertension with BP <120/70 mm Hg.