  We calculate quantum corrections to the entropy of four-dimensional de Sitter
space induced by higher-derivative terms in the gravitational action and by
one-loop effects. Employing the intertwinement in semiclassical gravity of
Euclidean de Sitter and anti-de Sitter saddles, we embed effective de Sitter
gravity theories in M-theory and express the entropy in terms of the
regularized Euclidean anti-de Sitter action on an auxiliary $\mathrm{EAdS}_4
\times S^7/\mathbb{Z}_k$ background. We conjecture that the partition function
of the holographically dual 3d ABJM CFT determines the explicit form of the
corrections to the de Sitter entropy. This includes a logarithmic term, the
coefficient of which, we show, agrees with an independent one-loop calculation
around the $-S^4 \times S^7/\mathbb{Z}_k$ Euclidean de Sitter saddle. This
provides evidence that the microscopic degrees of freedom behind the entropy of
four-dimensional de Sitter space in gravitational theories with a holographic
dual description are encapsulated by the path integral of the Euclidean CFT on
the three-sphere.
