Importance: Some studies have reported increasing stroke incidence at younger ages (<55 years) but have often relied only on administrative data, and more population-based studies of adjudicated stroke are required. An understanding of the drivers of any increase in incidence of young stroke also requires comparisons with stroke trends at older ages and with trends in incidence of other vascular events at younger ages. Objective: To determine temporal changes in incidence of stroke and other major vascular events at younger vs older ages. Design, Setting, and Participants: Prospective population-based incidence study conducted from April 2002 to March 2018 with a mean catchment population of 94 567 in Oxfordshire, England. Exposures: Calendar time, premorbid vascular risk factors, and occupation. Main Outcomes and Measures: Changes in incidence of stroke, transient ischemic attack (TIA), and other major vascular events (myocardial infarction, sudden cardiac death, and peripheral vascular events) stratified by age, sex, diagnostic workup, etiology, and severity. Results: A total of 2429 incident strokes were ascertained (mean age, 73.6 [SD, 14.4] years; 51.3% female). From 2002-2010 to 2010-2018, stroke incidence increased significantly among participants younger than 55 years (incidence rate ratio [IRR], 1.67; 95% CI, 1.31-2.14) but fell significantly among participants aged 55 years or older (IRR, 0.85; 95% CI, 0.78-0.92; P