A new and distinct cultivar of Chrysanthemum plant named `Yopatagonia`, characterized by its uniform and outwardly spreading plant habit; strong and freely branching growth habit; dark green-colored foliage; uniform flowering response and habit; can be grown as a disbud-type, spray-type or without bud removal; early flowering habit; large decorative-type inflorescences with elongated oblong-shaped ray florets; dark purple-colored ray florets; and good postproduction longevity with plants maintaining good substance and color for about three weeks in an interior environment.