Location: Los Angeles County, California

Named for George Islip, a Canadian prospector who moved to Los Angeles in the 1850's. He first inhabited the abandoned "halfway house" that Wilson constructed (then abandoned) along his lumber hauling trail in Little Santa Anita Canyon. Robinson notes that Islip planted a small grove of cherry, apple, pear and plum trees on a sloping bench just behind the hut. Later, mountaineer George Aiken joined him and together they rambled over the mountains, blazing new trails and clearing old Indian paths such as one connecting Barley flats to Charlton Flat They made some money by selling fruit to climbers on their way to "Wilson's Peak" and by making and shipping wood shingles down to the valley below. As their trees grew to maturity, the site was abandoned and came to be known as "Orchard Camp" a popular overnight campsite. According to Will Thrall, at some time before 1880, Islip became an early area homesteader on the west bank of lower San Gabriel Canyon and often wandered in the mountains near the peak that now bears his name. What is now known as Islip Saddle was the top of a main Indian cross-mountain trail through San Gabriel Canyon connecting the Gabrieleño and the Chemehuevis tribes.

Mount Islip later became a favorite retreat of James Guilford Swinnerton (1875-1974), who drew a very popular comic-strip called "Little Jimmy" for the Hearst syndicate. He became the first Southern California based commercial artist to gain national fame. There is a camp below the summit, where Swinnerton worked through the summers of 1890 to 1910. He painted a cartoon of his character on a tree and titled it "Little Jimmy Camp" (1909). This name was adopted by USFS surveyor Don McLain (1920).

A rock cairn on the summit was built by students led by "Pete" Goodell from Occidental College (1910). This was torn down (1926) to allow for the building of a lookout tower and a rock hut (1927-38).

Name first appears on USGS Rock Creek topo (1903).

Peak was on the original 1946 HPS Peak List. Weldon Heald climbed this peak in 1933.