Additional Information:

• World population hits 6 billion – US news – Only – September 1999 …
  Oct. 12, 1999 — The world’s population topped the 6 billion mark Tuesday, with the birth of a baby in Sarajevo. To some, that’s cause for celebration.
• 6 Billion and Counting-World Population – My Illinois StateOne of the great stories is the growth of world population over the last century and where this is going to go in the next few years.
• World population milestones – Wikipedia
  The United Nations Population Fund designated 12 October 1999 as the approximate day on which the world population reached six billion.
• World population – Wikipedia
  Thereafter, the global population reached four billion in 1974, five billion in 1987, six billion in 1999 and, according to the United States Census Bureau, seven billion in March 2012. The United Nations, however, estimated that the world population reached seven billion in October 2011.