O.O. Denny Park is a 46-acre (19 ha) park on the northeast shore of Lake Washington that is managed by the city of Kirkland, Washington but is owned by the city of Seattle. It has approximately 0.25 miles (400 m) of Lake Washington shoreline, and some park amenities such as BBQ grills and a covered structure at the shore, with mostly unimproved forest above the lake, surrounding Denny Creek.

Named for Seattle founder Arthur A. Denny's son Orion Orvil Denny (1853–1916), the site of present-day O.O. Denny Park served as Orion Denny's country estate. Orion Denny and his wife called their estate "Klahanie", which is Chinook for "out of doors." Following Orion's death in 1916, Denny's widow Helen willed Klahanie to the city of Seattle to become a public park named in memory of her husband.

The park opened to the public in 1922. In 1926, the park became a designated campsite for Seattle children. In 1954, the old Denny residence was torn down.

After 1968, Seattle turned management of the park over to King County. In 2002, management was taken over by the Finn Hill Park and Recreation District. The city of Kirkland began managing the park in 2013, following its annexation of the Finn Hill neighborhood. The park remains owned by the city of Seattle.

The park features an unusual quantity of trees over 150 feet tall, including grand firs, black cottonwoods, western hemlock, and cedars. Many Douglas firs stand over 200 feet tall, and are among the tallest trees in the Seattle area. One of the Douglas firs is "Sylvia", a 600-year-old specimen over 26 feet (7.9 m) in circumference, once the largest fir tree in King County; it was 255 feet (78 m) tall until the 1993 Inauguration Day windstorm topped it.

The park is one of four designated, protected bald eagle nesting areas in Kirkland, all on the Lake Washington shoreline.

• "Finn Hill Park and Recreation District hands over park operation to Kirkland city", Kirkland Reporter, April 3, 2013
• Alan J. Stein (December 5, 2002), "O.O. Denny Park", HistoryLink, Seattle: History Ink
• Stekel, Peter (2015). Best Hikes Near Seattle. Falcon Guides Best Hikes Near Series. Rowman & Littlefield. ISBN 978-1-4930-1435-4.
• Cathy McDonald (June 8, 2011), "Meet Sylvia the topless fir in Kirkland's O.O. Denny Park", The Seattle Times
• Aaron Kunkler (August 25, 2016), "County steps up to make two north Kirkland parks more accessable [sic]", Kirkland Reporter
• Weber, Andrew; Stevens, Bryce (2010), "O.O. Denny County Park Loop", Easy Hikes Close to Home: Seattle, Menasha Ridge Press, pp. 50–53, ISBN 9780897328395
• Bright, William (2007), Native American Placenames of the United States, University of Oklahoma Press, p. 228, ISBN 978-0-8061-3598-4, OCLC 53019644, retrieved January 16, 2017 – via Google Books
• City of Kirkland Department of Information Technology/Geographic Information System with annotation by Washington Department of Fish and Wildlife (January 30, 2018), "Sensitive areas map" (PDF), City of Kirkland official website, retrieved 2019-01-29

• Official website (City of Kirkland Parks)
• Trail map (Finn Hill Alliance, 2012)
• U.S. Geological Survey Geographic Names Information System: O O Denny Park
• O. O. Denny Park — Washington Trails Association