Plant decomposition and litter accumulation are important components of wetland functions, yet they have rarely been evaluated in created wetlands. In this study, eleven 20-yr and six 2-yr-old depressional wetlands, the most common type of created wetlands, were investigated. We measured plant decomposition as mass loss over 507 days for both age classes and litter accumulation as litter (detritus) mass present in the 20-yr-old wetlands. The wetlands were all created via excavation and contained shallow facultative wetland and deeper obligate wetland plant communities that were often dominated by Scirpus cyperinus and Typha latifolia, respectively. In the decomposition study, stems and leaves from each species were harvested from an adjacent 20-yr-old wetland site and placed in separate plastic mesh bags. Bags were deployed in March 1994 and were recovered after 2, 161, 258, 364, and 507 days. In the litter accumulation study, plant litter that accumulated on top of alluvium was harvested in 0.25-m² plots adjacent to decomposition bags. Several environmental variables were measured in the 20-yr-old wetlands, including live standing crop biomass (peak aboveground biomass) in 1993 and 1994, nutrient concentrations (in water, soil, and plant tissues), and hydrologic parameters. Decomposition was faster in 20-yr-old wetlands (76% of mass remaining) than in 2-yr-old wetlands (85%) but was well below most literature estimates for comparable species in natural wetlands (53%). Decomposition of S. cyperinus was slower than that for T. latifolia in all 17 wetlands. In the 20-yr-old wetlands, hydrologic variables were important for decomposition of both species. Masses of litter that accumulated during the 20 years since excavation were greater among facultative wetland (764 g/m²) than in obligate wetland communities (368 g/m²). Accumulated litter mass in the facultative wetland community was positively correlated with the S. cyperinus percentage of total live standing crop biomass. Accumulated litter mass in the obligate wetland community was positively correlated with drawdown duration and litter C:N ratios. Decomposition functions of these wetlands are still developing 20 years after creation.