Here's a link to excellent short descriptions of trails in Mt. Jefferson Wilderness, with each trail description accompanied by a sketch map that has links to photos taken along that trail:
http://www.nwhiker.com/JeffersonWilderness.html
To get to a trail description at the above link, click on a trail icon on the overview map of the Jefferson Wilderness, then roll mouse over camera locations shown along the trail to see the view at that location.
Jefferson Park can be accessed from several trail heads – from the west, there's a trail head at the end of White Water Road off of Santiam Highway (short distance from Detroit, about hour from I-5 at Salem); from the north, there's Park Ridge trail head starting at Breitenbush Lake; from the southwest there's Pamelia Lake trailhead; and from the south, there's the PCT via Hunt's Cove.
As shown by the map and descriptions at above link, there're an abundance of trails in the Jefferson Wilderness that can be combined to make a "hike into Jefferson Park" via several different loop or quasi-loop trips using trail heads at Whitewater Road, Pamelia Lake and Hunt's Cove, and Breitenbush Lake.
Jefferson Park can also be done as a fairly easy 10 mile day hike, although once there you would want to have several days to explore, fish, and just laze around.