Environmental temperature and an organism’s ability to respond to it are critical determinants of the geographic distribution of species. Nematostella vectensis is a burrowing sea anemone that inhabits estuaries along the Atlantic coast of North America from Nova Scotia (45°N) to Georgia (31°N). Like other estuarine species, N. vectensis is exposed to large daily (>20°C) and seasonal (>25°C) fluctuations in temperature, requiring wide temperature tolerances. At the same time, the natural distribution of this species spans a pronounced thermal cline, which may promote the evolution of different temperature optima and tolerances in populations. We tested the thermal tolerance of N. vectensis adult and developmental stages, which showed all life cycle stages had critical temperatures within 1°C (lethal temperature 39.5 to 40.5°C). When temperature tolerance values were compared with recorded field data, N. vectensis is living in environments very close to their physiological limit. We utilized common garden experiments (13, 21, and 29°C) to test for temperature-specific growth and regeneration rates in N. vectensis from different portions of this species’ range. Temperature had a significant effect on growth and regeneration rate in all clonal lines, with a significant negative relationship between latitude of origin and growth rate at 29°C. Individuals from higher latitudes did not exhibit higher growth rates at cooler temperatures. Together, our results show a combination of broad thermal tolerances for developmental and adult stages and evidence for local adaptation to higher temperatures in populations living in lower latitude locations that would be physiologically compromised with future warming.