Allen Mountain is a mountain in the Adirondacks in the U.S. state of New York. It is the 26th-highest of the Adirondack High Peaks, with an elevation of 4,340 feet. The mountain is located in the town of Keene in Essex County. It was named for Rev. William B. Allen by his friend, Rev. Joseph Twichell, while the two were visiting the Adirondacks in 1869. The ea…Allen Mountain is a mountain in the Adirondacks in the U.S. state of New York. It is the 26th-highest of the Adirondack High Peaks, with an elevation of 4,340 feet. The mountain is located in the town of Keene in Essex County. It was named for Rev. William B. Allen by his friend, Rev. Joseph Twichell, while the two were visiting the Adirondacks in 1869. The earliest recorded ascent of the mountain was made on August 21, 1921, by Bob Marshall, George Marshall, and Herbert Clark.