The 2021 Thoreau Tennis Open was a professional tennis tournament played on outdoor hard courts.

It was the second edition of the tournament which is part of the 2021 WTA 125K series.

The tournament had been upgraded from ITF 60K to WTA 125K, marking its first edition as a challenger event.

It took place in Concord, United States between 2 and 8 August 2021.

The following players received wildcards into the singles main draw: The following player received entry using a protected ranking: The following players received entry from the qualifying draw: The following player received entry as a lucky loser: The following pair received a wildcard into the doubles main draw: