Functioning ecosystems can buffer communities from many negative impacts of a changing climate. Flooding, in particular, is one of the most damaging natural disasters globally and is projected to increase in many regions. However, estimating the value of “green infrastructure” in mitigating downstream floods remains a challenge. We estimate the economic value of flood mitigation by the Otter Creek floodplains and wetlands to Middlebury, VT, for Tropical Storm Irene and nine other floods. We used first principles to simulate hydrographs for scenarios with and without flood mitigation by upstream wetlands and floodplains. We then mapped flood extents for each scenario and calculated monetary damages to inundated structures. Our analysis indicates damage reductions of 84–95% for Tropical Storm Irene and 54–78% averaged across all 10 events. We estimate that the annual value of flood mitigation services provided to Middlebury, VT, exceeds $126,000 and may be as high as $450,000. Economic impacts of this magnitude stress the importance of floodplain and wetland conservation, warrant the consideration of ecosystem services in land use decisions, and make a compelling case for the role of green infrastructure in building resilience to climate change.