In 1919, Charles and Jennie Lewis purchased a tract of land bordering Mahoning Creek in Valley Township. The Lewis's had one child, a son, named Robert.

The land would be destined to fulfill Jennie Lewis's dream to provide a place where children could go and enjoy themselves.

Before the opening in May 1927, the Lewises sponsored a contest to name the park into which they had put much hard work and planning. Mrs. Frank Irving, of Front Street in Danville, won the contest and received a season ticket "good for all the privileges of the pool for the Season of 1927". On July 4, 1927 the newly named Sunnybrook Park was opened.

Mae Hackenburg went to live with the Lewis family at the age of 14 and spent the rest of her life working and caring for Sunnybrook Park. According to an article written by Mrs. Hackenburg about the opening of Sunnybrook Park: "The facilities consisted of the pool, bathhouse, concession stand, one picnic pavilion, swings, a monkey gym, a merry-whirl, and a miniature golf course. Later, there were two cabins added and two more picnic pavilions beside the creek and one up on the hill beside the golf course."

"The swimming pool was the main attraction of the place that was to gain fame as Sunnybrook Park. Nine feet deep at the deepest end, it tapered to three feet at the lower end. It was painted bright blue and was surrounded by sand. There were two diving boards and a lifeguard stand and who could ever forget the ROPE that separated the deep end from the shallow, where on which the swimmers swung and practiced swimming strokes."

According to Kay Sharrow, the Lewis's granddaughter, there were baskets with locks that could be rented to put clothes into when the swimmers changed. A key was given to the swimmers so their possessions were kept safe. When the Lewises had the park, the key was pinned to the swimmer's bathing suit, later an elastic band was used and the key was placed around an arm or leg for safe keeping. Bathing suits were also available to borrow if needed.

On May 23, 1955, Robert Lewis and Ruth, his wife, and Charles and Jennie Lewis sold the park to a non-profit corporation called The Danville Playground Association for the sum of $20,000.00. The Danville Playground Association, which is made up of a board of volunteers, managed the park.

On June 21, 1972, hurricane Agnes devastated Sunnybrook Park. However, by July 1, the Playground resumed operations as a day care center, and the pool reopened on July 2, 1972.

In 1975, the Danville Playground Association began looking into replacing the pool at Sunnybrook Park. After much discussion and many delays, on May 11, 1977, construction was started by a general contractor, C.F. King of Sunbury, on an "L" shaped pool. The pool was 25 meters in length and touted as "Olympic" size.

The newly constructed swimming pool was opened on July 6, 1977. A formal dedication was held on Sunday, July 24, 1977, with Representative Daniel J. Flood and Senator Franklyn L. Kury cutting the ribbon. The pool was named for Dorothy M. Bonawitz. Miss Bonawitz had served as secretary of the Danville Playground Association, Inc. and had spearheaded the idea of constructing a new pool and worked tirelessly to obtain funds to build it.

On October 25, 2000, an agreement between the Danville Playground Association and the Valley Township Supervisors was signed. This agreement enabled the Sunnybrook Board to apply to the Department of Community and Natural Resources for grant monies for new playground equipment. The $40,000.00 project is located near the entrance to the Park and was finished in time for the celebration of Sunnybrook Park's 75th year. Special thanks to the volunteers from Strick Corporation (now Great Dane), Valley Township Supervisors, Valley Township Road Foreman, and members of the Danville Playground Association for assisting in the placing of the equipment. Other improvements to the park which were done by Eagle Scouts and their families, members of the 4H Club, Valley Township and the Sunnybrook Park Board volunteers include siding the bathhouse, new ladders, painting the pool, replacement of roof on pavilion #2, improvements of the road into the park, clean up, and planting flowers.

In 2003, the Danville Playground Association no longer managed Sunnybrook Park.  A Board of Directors was formed and began managing the park.

The Sunnybrook Park Board of Directors appreciates that for more than 30 years the United Way has been a continuing financial supporter of Sunnybrook Park.