Despite being the highest point on the 40+ km long Persimmon Range, Mount Persimmon has no recorded ascent that I could find. We (Warren, Jenise and Paul Finlay) successfully ascended it on July 18, 2018, plus two nearby unnamed summits on July 17, 2018. With no motorized access of any kind allowed in Willmore Wilderness Park, reaching these summits required following ridiculously muddy horse trails up the Wildhay River from the Rock Lake trailhead, where we branched off on a trail that heads up Persimmon Creek. After another junction, the trail became faint and nearly grown over in dense willows when it headed to the creek bed from an empty horse-riders' campsite. We then followed Persimmon Creek, with an overgrown trail appearing now and then, but otherwise following game trails or bushwhacking, with several creek crossings to avoid steep banks.

Upon reaching the upper valley, we bushwhacked through dense willow and spruce to find a somewhat flat place to set up base camp in the meadows just below treeline. Having seen many grizzly bear and wolf tracks on the way in, but no trees to hang food at base camp, we hung our food from nearby cliffs at night. After a 3 day approach, on day 4 we attempted to ascend Mount Persimmon by climbing nasty scree to reach the SW ridge above a gendarme above the pass at the end of Persimmon Creek valley. However, we were turned back by a chossy knife edge at 2740m. We then descended back to below the pass, and then traversed across scree and instead climbed up scree to reach the summits of two unnamed peaks immediately SW of Mount Persimmon. GRS 826356 did not have a cairn, so this may be its first ascent. Summit GRS 826363 had an existing cairn. Topo maps show the south summit as higher, but it was clear to us (and our GPS) that the north summit was slightly higher.
The next day we chose to attempt Mount Persimmon instead via its south face. Ascending the south face from the upper Persimmon Creek valley, we were able to work our way up ugly scree around cliff bands as we gained altitude, with various ups and downs (and snow slope crossings steep enough that an ice axe would be nice) as we followed the undulating cliff faces. This allowed us to gain the SW ridge above the obstacle that stymied us the previous day. At this point, we ascended talus to the summit.
A large cairn was already present on the summit, although it looked more like an old surveyor's cairn than a climber's cairn, since the rocks were unusually large. Who placed this cairn, and how they got there is unknown to this author. With rain in the forecast, we decided to get out before the way back became any muddier, taking two days to retrace our steps back to the trailhead.