Irish academic Paul Tempan records that Knocknahillion derives its name from Cnoc na hUilleann Thair, which is the name of a nearby townland, that translates as "peak of the west elbow"; however the translation is apt given the positioning of the peak, which is to the west of the central spine of the Maumturks range at point at which the range turns to a more south-easterly direction.
Geography
Knocknahillion is in the middle sector of the long north-west to south-east central spine of the Maumturks range in the Connemara National Park. To the north, Knocknahillion is connected to Letterbreckaun, the 2nd highest peak in the range at, by a high winding rocky ridge that includes the subsidiary peak of Knocknahillion North Top at, whose prominence of qualifies it as an Arderin. Further along this ridge lies the minor peak of Barrlugrevagh at, whose prominence of qualifies it as an Arderin Beg. To the southeast of Knocknahillion is the col of Maumahoge, which then rises up again to the corrie lake of Lough Maumahoge, and eventually to Binn idir an dá Log, the highest mountain in the range at.
Hill walking
The easiest way summit Knocknahillion is a 5-kilometre 2-3-hour route via the pass of Maumahoge; however, because of its positioning on the high rocky central spine of the central Maumturk range, it is also summited in a longer 14-kilometre 5-6 hour loop-route starting at the col of Maumahoge in the south, climbing Knocknahillion and then along a winding 2-kilometre rocky ridge to the top of Letterbreckaun, before descending via the sharp "v-shaped" col of Maam Turk, from which the entire range bears its name. Knocknahillion is also climbed as part of the Maamturks Challenge, a 25-kilometre 10–12 hour walk over the full Maumturks range, which is considered one of the "great classic ridge-walks of Ireland", but of "extreme grade" due to the circa 7,600 feet of total ascent; however, because the peak of Knocknahillon is offset to the west of the core winding rocky ridge, it is not always summited during the challenge.
Rock climbing
While the Maumturks range is not particularly known for rock climbing routes, some have been developed at a crag just below and west of Lough Maumahoge, with routes of 90 to 190 metres at climbing grades of S to HVS.
