Coastal marshes can have high rates of carbon (C) accumulation associated with high primary productivity and sedimentation rates, and low rates of microbial decomposition. Mitigation for the loss of saline marshes by restoration and creation is becoming widespread; however, a greater understanding of the timescale and capacity for these new sites to function as C sinks is needed. For this study, we examined a chronosequence of six created coastal marshes ranging from 0 to 32 years old and two adjacent natural marshes in Sabine National Wildlife Refuge in the Chenier Plain of Louisiana. We collected soil cores in created and natural marshes (n = 6) and measured bulk density, total organic C and nitrogen (N), particle size, organic matter content, and fatty acid methyl ester relative abundances in all cores. To calculate longer-term carbon accumulation rates (LCAR), we used the known age of created marshes and measured Cesium-137 in natural marsh cores. Short-term carbon accumulation rates (SCAR) were measured using feldspar marker horizon plots. Relationships among soil C accumulation, microbial communities, and environmental factors, including vegetation, salinity, hydrology, and elevation, were also examined. Created marshes LCAR ranged from 18 to 99 g C m-2 yr-1, and did not significantly differ among marshes of different ages (p > 0.05). We observed high spatial variability of both SCAR and LCAR within created marshes, with stem density contributing the most to the variability in created marsh LCAR (p = 0.01). All marshes contained distinct microbial community compositions (p < 0.001), with soil C to N ratio associated with higher total microbial abundance, and plant species, elevation, and marsh age associated with shifts in dominant microbial groups. The data suggest that the establishment of vegetation with high stem densities, such as Distichlis spicata and Spartina patens, may facilitate higher LCAR in created marshes, which may be of interest for project planning in relation to C credits. This study also provides foundational information regarding microbial community dynamics in created wetland soils, which will support future research on the links between community composition and ecological processes such as blue C accumulation.