Type 1 diabetes is one of the most common chronic diseases of childhood in the United States, although it can manifest at any age. In 2017, based on data from the SEARCH for Diabetes in Youth study (SEARCH), the overall prevalence of type 1 diabetes among U.S. youth age <20 years was 215 cases per 100,000 population. Type 1 diabetes prevalence was similar by sex but increased with age. In 2017–2018, the annual incidence of type 1 diabetes in youth <20 years was 22.2 per 100,000, representing an annual increase of 2.02% since 2002–2003. Among non-U.S. youth, the prevalence of type 1 diabetes varies widely and was lowest in Burkina Faso, Africa (1.76 per 100,000 in 2022) and highest in Qatar, in the Middle East (386.2 per 100,000 in 2018–2020). In 2022, the lowest incidence was reported in Burkina Faso, Africa (0.34 per 100,000) and the highest in Sardinia, Italy (76.3 per 100,000). Compared to data in youth, data on the prevalence and incidence of type 1 diabetes in U.S. adults are very limited. According to the National Health Interview Survey (NHIS), the prevalence of type 1 diabetes in adults age ≥20 years in 2019–2023 was 390 per 100,000 population. The higher prevalence in adults compared to children is expected, as it comprises individuals diagnosed in both childhood and adulthood. Furthermore, recent data suggest that type 1 diabetes incidence in adults may be at least as high as in children, challenging the historical belief that type 1 diabetes is primarily a childhood disease. Specifically, data from a California healthcare system database estimated that the annual incidence in adults age 20–45 years was 30.1 per 100,000 population in 2017 and was higher in men (32.5 per 100,000) compared with women (27.2 per 100,000). Additional studies on incidence in adults are critically needed to better understand the growing burden of type 1 diabetes in the United States. Among non-U.S. regions reporting data on the incidence of type 1 diabetes among adults, overall rates ranged from 3.84 per 100,000 in China (2021) to 32.07 per 100,000 per year in Ireland (2011–2016). Although vital for determining the burden of type 1 diabetes in the population and guiding effective prevention and control strategies, surveillance of type 1 diabetes faces challenges, particularly given the absence of standardized case definitions and consistent ascertainment methodologies. Administrative and electronic health record databases may serve as tools for estimating diabetes incidence and prevalence; however, while these databases offer promising opportunities, their reliability and validity remain uncertain and require further investigation. Ultimately, standardizing diabetes classification and improving data ascertainment are critical steps toward improving our understanding of the growing burden of type 1 diabetes and developing effective mitigation strategies.