We describe an algebra of observables for a static patch in de Sitter space,
with operators gravitationally dressed to the worldline of an observer. The
algebra is a von Neumann algebra of Type II$_1$. There is a natural notion of
entropy for a state of such an algebra. There is a maximum entropy state, which
corresponds to empty de Sitter space, and the entropy of any semiclassical
state of the Type II$_1$ algebras agrees, up to an additive constant
independent of the state, with the expected generalized entropy
$S_{\text{gen}}=(A/4G_N)+S_{\text{out}}$. An arbitrary additive constant is
present because of the renormalization that is involved in defining entropy for
a Type II$_1$ algebra.
