Windstorms are a major natural hazard in many countries. The objective of this study is to identify and characterize intense windstorms during the last four decades in the U.S. Northeast and determine both the sources of cyclones responsible for these events and the manner in which those cyclones differ from the cyclone climatology. The windstorm detection is based on the spatial extent of locally extreme wind speeds at 100 m height from the ERA5 reanalysis database. During the top 10 windstorms, wind speeds in excess of their local 99.9th percentile over at least one-third of land-based ERA5 grid cells in this high population density region of the U.S.. Maximum sustained wind speeds at 100 m during these windstorms range from 26 to over 43 ms-1, with wind speed return periods exceeding 6.5 to 106 years (considering the top 5% of grid cells during each storm). Property damage associated with these storms, inflation adjusted to January 2020, ranges from $24 million to over $29 billion. Two of these windstorms are linked to decaying tropical cyclones, three are Alberta Clippers and the remaining storms are Colorado Lows. Two of the ten re-intensified off the east coast leading to development of Nor’easters. These windstorms followed frequently observed cyclone tracks, but exhibit maximum intensities as measured using 700 hPa relative vorticity and mean sea level pressure that are five to ten times mean values for cyclones that followed similar tracks over this 40-year period. The time-evolution of wind speeds and concurrent precipitation for those windstorms that occurred after the year 2000 exhibit good agreement with in situ ground-based and remote sensing observations, plus storm damage reports, indicating that the ERA5 reanalysis data have a high degree of fidelity for large, damaging windstorms such as these. A larger pool of the top 50 largest windstorms exhibits evidence of only weak serial clustering which is in contrast to the relatively strong serial clustering of windstorms in Europe.