Marsh foraminifera are useful indicators of relative sea level rise and their populations in marsh peat sediments can be used to estimate rates of relative sea level rise. We studied marsh foraminifera in cores from Great Island, on the eastern side of the Connecticut River Estuary, and from Knell's Island, on the eastern side of the Housatonic River Estuary. Both cores are located in marshes close to a major source of fresh water, but at different tidal ranges. We dated the cores using ²¹⁰Pb and ¹⁴C, and obtained records of metal pollution. We sliced the cores in samples of 2.5 to 5 cm thick, and used the benthic foraminiferal zonation in the intertidal zone of the marsh to determine the paleo-elevation of each sample with respect to mean high water. We then used the age and benthic foraminiferal information to derive the rates of relative sea level rise at the core sites. Rates of relative sea level rise (RSLR) were similar in both cores, and also similar to rates determined for other cores along the northern shore of Long Island Sound. Between about 1000 AD and 1600 AD these rates of RSLR were about 1.3 mm/year. At about 1600 to 1650 AD the rates increased to about 2.8 mm/year until the present time. At the time of increasing rates of RSLR in the 17^th century, however, the marshes at the core sites along both rivers did not drown, but in contrast, built up from lower-middle marsh to higher marsh. We do not know whether these increased rates of marsh build-up reflect conditions within the marshes or within the larger watersheds of the rivers, e.g. as the result of increased sediment transport.