Petaluma’s earliest parks were disorganized and mostly untended plots of land until a dedicated group of women formed the Ladies’ Improvement Club with the goal of improving two town plazas. The club’s first meeting was at Miss Shattuck’s newspaper office in 1896. Petaluma's former historian, Ed Mannion, described the event this way:

Among those at the meeting were the matronly Mrs. A.A. Atwater and Mrs. C.H. Northrup, the dedicated Miss Kittie Weston, Miss Annie Tibbets, Miss Estelle Newburg and Miss Zoe Fairbanks, the pretty Miss Emma Palmer, and the handsome and sophisticated poetess Mrs. C. E. Reed.

The park, then known variously as “Upper Plaza”, “Hill Plaza,” and simply “the Plaza,” had been set aside as a public space in the 1852 plat for the town. It must have been in terrible condition after decades of neglect; among the first accomplishments of the club were the removal of fifteen old trees stumps and three cartloads of tin cans. The women of the club, being "ladies," could not do the physical work of improvement themselves but within the first year they had solicited bids to install gravel paths in the park. 

Historic images suggest the paths in the park now are roughly the same layout as those the Ladies established. The first paths were gravel lined with stones (stone appear to have been granite setts); now crumbling asphalt coats the paths.

In 1898 the Ladies were seeking donations for benches and trees. Fifty palm trees were donated. Deciduous trees were also planted, and the parking strip along Kentucky Street was planted. The park was quite stuffed with trees in the early days. Some of these trees remain. 

 Speculation and other uses for the plaza were proposed up until the 1960s, whether for commercial uses (1865), a school (1887), or for parking. Some of the land was chopped off at Mary Street for hitching horses, and more was removed in 1962 for parking cars.

As early as 1928 the park was used as a location for a memorial for war veterans of Petaluma. A World War One memorial was designed by Roy M. Evens, and installed by Evans and Sons in 1929. In 1949 two small guns replaced the cannon, causing consternation among some in town, including the designer of the first memorial. It was felt that the small guns lacked the scale of the original cannons. The memorial is still in place, although nearly obscured by flanking yew trees.

The park was named Hill Plaza by the Ladies Improvement Club, and it went by that name until 2001 when the park was renamed for Richard Penry. Penry received the Congressional Medal of Honor for heroism he showed during the Vietnam War. A bronze plaque on a concrete and flagstone base was installed in his honor.

There is additional information on the park, as well as historic images, below: 

Penry Park - Deep History