Forest Park is a public municipal park in the Tualatin Mountains west of downtown Portland, Oregon, United States. Stretching for more than 8 miles on hillsides overlooking the Willamette River, it is one of the country's largest urban forest reserves. The park, a major component of a regional system of parks and trails, covers more than 5,100 acres of …Forest Park is a public municipal park in the Tualatin Mountains west of downtown Portland, Oregon, United States. Stretching for more than 8 miles on hillsides overlooking the Willamette River, it is one of the country's largest urban forest reserves. The park, a major component of a regional system of parks and trails, covers more than 5,100 acres of mostly second-growth forest with a few patches of old growth. More than 80 miles of recreational trails, including the Wildwood Trail segment of the city's 40-Mile Loop system, crisscross the park.