In order to enhance our understanding of the evolutionary history of squirrel monkeys (Saimiri spp.), we newly sequenced and analyzed data from seven complete mitochondrial genomes representing six squirrel monkey taxa. While previous studies have lent insights into the taxonomy and phylogeny of the genus, phylogenetic relationships and divergence date estimates among major squirrel monkey clades remain unclear. Using maximum likelihood and Bayesian procedures, we inferred a highly resolved phylogenetic tree with strong support for a sister relationship between Saimiri boliviensis and all other Saimiri, for monophyly of Saimiri oerstedii and Saimiri sciureus sciureus, and for Saimiri sciureus macrodon as the sister lineage to the S. oerstedii/. S. s. sciureus clade. We inferred that crown lineages for extant squirrel monkeys diverged around 1.5. million years ago (MYA) in the Pleistocene Epoch, with other major clades diverging between 0.9 and 1.1. MYA. Our results suggest a relatively recent timeline of squirrel monkey evolution and challenge previous conceptions about the diversification of the genus and its expansion into Central America.