Park at the small road-side pull-off on Cook-Underwood Rd and then cross the street to head 0.2 miles up Jackson Rd. Look for a old forest road at a fork on the right: this is where the trail begins. The trail will follow some gentle old farm roads through meadows along switchbacks before entering forest. From here the trail will continue a steady climb on easy to follow old road until you come to an intersection at about 1.8 miles. This intersection begins the loop part of the lollipop.
Note: You can follow the faint trail straight ahead (east) and do the loop counterclockwise which is recommended if the trail appears faint or it's likely to be overgrown in the summer (this is how this description is mapped). The trail part can be difficult to follow and going counterclockwise will help you navigate it back to the road section. However, it should be noted that the western half of the loop along the old road is not very good hiking - it's pretty boring really - so you may want to do that part first! It would also be shorter to do Cook Hill as an out-and-back to save some time/distance but then you'd miss the Adams views from the power lines.
From the intersection head east on the narrow foot path. You'll shortly enter mossier forest than the road up passed through and then enter a meadow in about 2.1 miles. These meadows can be covered with balsamroot in spring. Re-enter the forest and follow the trail onto the SE ridge of Cook Hill. From here the trail is very steep! Eventually you'll exit the forest into the upper wildflower-filled meadow which signifies you're close to the summit. The summit is wide open to the south offering great views of Mt Hood, Mt Defiance, and Dog Mountain (which is slightly lower than this summit) but there aren't views north.
Head down from the summit on a steep descent that soon turns into a mellow old forest road. Follow this to a radio tower, pass around the tower, and take the utility road to the power lines. From here a great view of Adams can be had and the Tin Can Trail
can be found. Look for another old road to the south that heads back into the forest. Follow this road all the way back to the intersection where the trail "ends" and then continue the remaining 1.8 miles to Jackson Road.
In total this hike is about 8.15 miles round trip counting the road, and nearly 3,000 of gain to a 3,015 foot high summit.