According to Pacific Crest Trail Association, this hiking route is 4,286 km (2,663 mi) long, passing through 25 national forests and 6 national parks. Around 4,265 km (2,650 mi) are in the USA, and the few miles left, in Canada.
Guinness Book of World Records designated it the longest hiking trail in the world. There is a competitor to this title though, the Continental Divide Trail, which will be crossing the USA from North to South on a distance of 5,000 km (3,100 mi). This trail is not yet completed. Therefore, Pacific Crest Trail is the winner at the moment.
Pacific Crest Trail starts in California, USA, and ends in British Columbia, Canada. Let's not forget the Pacific Crest Bicycle Trail, which runs almost parallel to the PCT on roads, and is a true Mecca for cyclists.
PCT passes the following 6 national parks: Kings Canyon National Park in California, Yosemite National Park in California, Lassen Volcanic National Park in California, Crater Lake National Park in Oregon, Mount Rainier National Park in Washington, North Cascades National Park in Washington.