Harmony Grove was located on the shores of Farm Pond in the southern section of Framingham. It had boating facilities and areas for strolling, for playing games, and for holding large outdoor meetings, a combination making it a popular spot for gatherings of temperance, abolition, and other social reform societies active at the time. From 1846 to 1865 the Massachusetts Anti-Slavery Society celebrated the Fourth of July with a picnic and rally at this spot, also referred to as Island Grove and Framingham Grove.
Excerpt taken from Thoreau lecture 43.
William Garrison and Henry David Thoreau were pretty involved in the anti-slavery movement in Massachusetts and they both took part in a famous anti-slavery rally at Harmony Grove on July 8, 1854. You can find more information about that rally and Thoreau's involvement by reading Thoreau lecture 43.
Harmony Grove was supposed to be a natural amphitheater, so if you go there today and stroll down Beech Street toward Franklin Street from Union Avenue, you can kinda see (to your left) a depression.
Harmony Grove was located between Farm Pond and Union Avenue. Thanks to County Atlas of Middlesex, F. W. Beers, 1875.