A regionally significant population of the rare Emydoidea blandingii (Blanding's Turtle) at Great Meadows National Wildlife Refuge (GM) in Massachusetts declined in numbers of individuals of >110 mm SCL from an estimated 135 in 1973 to ∼54 in 2004, when we began a long-term conservation management program for this population. In the early years of our efforts, the majority of females in the population were older individuals, mostly marked as adults in the 1970s (and thus >50 years old), and juveniles appeared scarce. In response, we began protecting Blanding's Turtle nests at GM in 2003 and began headstarting hatchlings and releasing them back into the population regularly in 2007. By the end of 2023, we had released 683 headstarted juveniles into the GM wetlands. Using data from nearly 20 years of population monitoring, including 430 turtle-years of radiotelemetry, we estimate that the number of Blanding's Turtles >110 mm SCL at GM has increased significantly during that period. Our 2023 population estimates, derived from an integrated capture–recapture model (using trapping and telemetry data) and a known-fate model (telemetry only) suggest that the population has nearly quadrupled (204 individuals, 95% CI = 176–240) or sextupled (316 individuals, 95% CI = 185–442), respectively, when compared to the 2003 estimate (54 individuals). Trapping data also support the conclusion that headstarting has greatly augmented the GM Blanding's Turtle population, with the population skewing younger and catch-per-unit-effort climbing throughout this effort.