Mangrove forests are among the world’s most productive and carbon-rich ecosystems. In addition to providing important fish and wildlife habitat and supporting coastal food webs, these coastal wetlands provide many ecosystem goods and services including clean water, stable coastlines, food, recreational opportunities, and stored carbon. Despite a growing understanding of the factors controlling mangrove soil carbon stocks, there is a pressing need to advance understanding of the pace of peat development beneath maturing mangroves — especially in created and restored mangroves, which are often intended to compensate for ecosystem functions lost during mangrove conversion to other land uses. To better quantify the rate of soil organic matter development beneath created, maturing mangroves, we measured ecosystem changes along a 25-year chronosequence in Tampa Bay Florida (USA). We compared ecosystem properties in created mangroves to adjacent natural mangroves. We also quantified site-specific changes that occurred between 2010 and 2016. Our objective was to advance understanding of the pace of ecosystem development in created, maturing mangrove forests. This information can improve predictions of mangrove responses to global change and ecosystem restoration.