Gerber staked an early claim to the 300 millionth American hoopla, and is holding some sort of contest or promotion with big prizes for someone. I have no idea, but I'm sure Google will help you.
They're basing the whole thing on an algorithm maintained by the US Census Bureau, which is rather inaccurately described as a population clock:
The clock is an estimate based on an algorithm that takes into account births, deaths and immigration. The bureau collects monthly birth and death numbers from the National Center for Health Statistics, Bernstein said. Net immigration is derived from the American Community Survey, an annual polling of several million U.S. residents.Though the "clock" has 40% of US population growth coming from immigration and naturalization, I'll go out on a limb and predict that the probability of Gerber's 300 Millionth American [sic] being a non-newborn is exactly 0%. The likelihood that he/she is named Gyllenhaal-Saarsgard, however, is another story.
Right now the formula is one birth per seven seconds, one death per 13 seconds and one net increase in immigrants per 30 seconds. With the number of deaths subtracted from the number of births, immigration accounts for about 40% of population growth.
The Census Bureau hasn't forecast the day the milestone will occur, but the algorithm points to Oct. 16.
And while the who and where are purely speculative, that hasn't stopped academics from theorizing [ed.: especially when asked to by LA Times reporters].
[like 10-min later update: see, people? This is what happens when I try to make a celebrity baby joke. the Gyllenhaal-Saarsgaard baby was born last night.]