Unfortunately the tree appears to be beyond recovery, and likely has been declining for several years, even if the symptoms were less prominent. It's hard to diagnose from the photos, but root damage or dieback, Hemlock Woolly Adelgid, scale insects, and mites are all possible contributors, though likely overlapping rather than by themselves (other than root issues). Soil conditions that can weaken hemlocks include heavy compaction from frequent foot traffic, poor drainage or excessive wetness, drought (if not watered), injury from construction or utility digging, and a soil acidity level (pH) outside the plant's ideal range, which is somewhat acidic. (For example, if a lawn or several plants in its root area routinely had lime applied over the years.)

Miri