  We describe KMS and ground states arising from a generalized gauge action on
ultragraph C*-algebras. We focus on ultragraphs that satisfy Condition~(RFUM),
so that we can use the partial crossed product description of ultragraph
C*-algebras recently described by the second author and Danilo Royer. In
particular, for ultragraphs with no sinks, we generalize a recent result by
Toke Carlsen and Nadia Larsen: Given a time evolution on the C*-algebra of an
ultragraph, induced by a function on the edge set, we characterize the KMS
states in five different ways and ground states in four different ways. In both
cases we include a characterization given by maps on the set of generalized
vertices of the ultragraph. We apply this last result to show the existence of
KMS and ground states for the ultragraph C*-algebra that is neither an
Exel-Laca nor a graph C*-algebra.
