Saltmarsh habitats sequester significant amounts of carbon from the atmosphere and provide vital habitats for various bird species but are eroding at increasingly rapid rates due to ongoing sea level rise. Yet, in some regions where space and topography permit, saltmarshes are transgressing into adjacent uplands, counterbalancing the lost area. In these areas, a greater proportion of saltmarsh is relatively young but it remains uncertain whether younger marshes support the same plant and animal communities as older ones. We compared soil organic matter (SOM), plant communities, and bird occupancy at 133 marsh patches on the Delmarva Peninsula, Virginia, USA. Marshes that converted from uplands since the early to mid-20th century exhibited lower SOM levels, were more closely situated to trees and snags, and were less likely to support obligate saltmarsh nesting bird species. Areas with past agricultural activity, characterized by features like berms and ditches, exhibited higher SOM levels, supported fewer of the most salt-tolerant plants and more of the least salt-tolerant species, and were more likely to support saltmarsh obligate bird species. We expect areas where a high proportion of relatively young marsh to shift away from the most salt-tolerant plants and birds, especially where an agricultural legacy can be found. We hypothesize that elevated organic carbon content found in formerly farmed fields may result from decreased inorganic sediment input, facilitated by restricted tidal flooding, rather than an enhanced capacity for carbon sequestration. However, further investigation is necessary to conclusively address this issue.