Establishing records of mercury (Hg) accumulation at sensitive sites provides an important means of assessing previous environmental conditions and historic Hg inputs from atmospheric deposition. Robust records of Hg deposition can also be important for evaluating legislation on atmospheric loading, and for predicting future needs. Lake sediment archives from undisturbed environments have been found to be the most reliable records of Hg accumulation rates. However, while sediment Hg records in some regions are well-established, the geographic distribution of deposition archives across the North American continent is sparse and coastal sites along the Eastern United States present an important data gap. In this work, we assess Hg accumulation in lake sediments at two coastal National Parks in the Northeast U.S. - Acadia National Park and Cape Cod National Seashore, and apply Hg isotopic signatures to investigate the sources and processes mediating deposition at each site. Records at both sites showed increasing rates of Hg accumulation since pre-industrial times. Hg concentrations in Acadia increased ~4 times since the early 1800’s and peaked in the 1970’s, whereas concentrations in Cape Cod ponds continued to increase in recent years reaching levels ~8 times higher than 200 years ago. The decreased flux of Hg in the past ~40 years in Acadia is consistent with reduced atmospheric Hg emissions and has been observed at other sites, however the ongoing elevated Hg flux at the Cape Cod site suggests continued watershed inputs of Hg, despite a minimal watershed area. Isotopic signatures of Hg in both Acadia and Cape Cod ponds show a large positive shift in δ²⁰²Hg with industrialization and subsequent decrease in recent years at the Acadia site only. Previous studies have suggested this shift is due to increased wet relative to dry deposition of Hg. A coinciding large positive shift in Δ¹⁹⁹Hg (from -0.5 ‰ to -0.005 ‰) occurred at the Acadia site, whereas Δ¹⁹⁹Hg values were relatively constant (from -0.1 ‰ to 0.04 ‰) over time in the Cape Cod site. The positive shift in Δ¹⁹⁹Hg at Acadia also suggests a change in atmospheric deposition, whereas the shift in δ²⁰²Hg but not Δ¹⁹⁹Hg suggests a potential marine influence at this site. The differences in these two coastal records emphasize the role of landscape and location on the processes controlling Hg flux in lake sediment archives. The reduction in Hg flux may lag atmospheric emissions where residence time in the catchment is long.