The 7-valent pneumococcal conjugate vaccine (PCV7) was added to the U.S. infant immunization schedule in the year 2000. By 2009, PCV7 introduction was associated with a 43% decline in all-cause pneumonia among U.S. children aged <2 years. In 2010, a new 13-valent pneumococcal conjugate vaccine (PCV13) replaced PCV7 in the infant immunization schedule, expanding protection from seven to 13 pneumococcal serotypes. To examine changes in all-cause pneumonia hospitalizations among children aged <2 years after the switch to PCV13, Tennessee hospital discharge data for 1998-2012 were analyzed. By 2012, all-cause pneumonia hospitalizations in children aged <2 years had declined an additional 27%, relative to the PCV7 years. Pneumonia hospitalizations were estimated to be 4.1 per 1,000 population in 2012, a historically low rate that represents a 72% decline from the rate before PCV7 introduction. Tennessee children aged <2 years experienced about 1,300 fewer pneumonia hospitalizations annually in 2011 and 2012 than in the years before pneumococcal conjugate vaccine (PCV) use. These data attest to the powerful impact of the PCV program on pneumonia in Tennessee children. The observed trend likely represents a major decline in pneumococcal pneumonia, which should stimulate a reassessment of current causes and appropriate management of pneumonia in children.