This chapter examines Classic to Postclassic population dynamics throughout the tenth b’ak’tun in the Belize River Valley to explore the topic of demographic decline in greater depth. It also examines patterns in archaeological, epigraphic, and isotopic data from human remains to understand changing population dynamics in Belize Valley at the end of the Classic period. The chapter identifies evidence for rapid population decline that corresponds to an increase in atypical burial patterns and non-local strontium isotope signatures at the sites of Baking Pot, Barton Ramie, and Cahal Pech. The Belize Valley is best-known as the location of Gordon Willey’s pioneering settlement archaeology research of the 1950s. The Early Classic period is not well-understood in the Belize River Valley, to great degree because local Preclassic ceramics were not rapidly or completely replaced by Tepeu sphere pottery. An impressive number of elaborate Late Classic royal and elite tombs containing a wealth of imported grave goods also have been identified at Baking Pot.