Data Source
I found the data at the census.gov website. I encourage you to visit their site and verify the numbers for yourself, and to even try your own hand at predicting the trends.
Interestingly you will find that starting in the 1960s, the Census Bureau keeps changing their methodologies of data collection as well as the format of the data itself. This can be a bit frustrating, but I think it is related to the almost cataclysmic shift in demographics that occurs in the period from 1965 onward.
Forecasting Methodology
The estimates for the future are based on the trendlines starting with the 1960 census through the 2000 census. I did a straight line projection of the numbers by dragging over the columns in an Excel spreadsheet. Blame Microsoft if you don't like the results I guess (FYI, Microsoft lobbies heavily for increased immigration). The trend is an accelerating one through the 2000 census which is why the graphs curve upwards.
Estimates Are Conservative
Since the 2000 census, the rate of immigration both legal and illegal has accelerated beyond the previous trends, and this is not factored into the future estimates. For example, the Census Bureau official estimates for the future predict total USA population of 308 million by 2010, but as of the end of 2005 we are already 60% towards this goal. And errors at the beginning of a prediction will have amplified effects on the later numbers.
The estimates also do not specifically account for the low birth rates of Caucasians, and corresponding higher birth rates of black Americans and immigrants, beyond what is already implied by the 1960 to 2000 trend.
The estimates also do not account for the passing of the baby boomer generation over the next 10+ years. I have seen projections on the internet for a majority non-Caucasian America ranging from 2025 to 2035, with overal Caucasian population going flat or even shrinking. Even if you think my estimates are off, the official Census Bureau predictions are for a majority non-Caucasian America by 2050. I think this estimate is very conservative and serves an upper threashold. But it also validates the fact that the prediction made by this site is at the very least somewhat on target.
Why Just Caucasians?
It certainly would be nice to know the growth and decline of black and Indian populations by state. Unfortunately the data isn't there. Most Indian populations (which were actually quite sparse as a result of 100 years of disease starting with Spanish exploration in 1492) in the west lived in territories not yet formed as states, and are thus uncounted. In the states where they are counted, they are lumped together with the black population and Asian populations. In other cases, Indians are uncounted entirely. Being that the Caucasian population is the only constant for the entire history, it is the only number that has any real meaning in the context of a historical timeline. In light of this, the 'Other' category really makes the most sense as a comparative tool.
Data for Hispanics, Asians, and other racial and ethnic minorities only becomes available in the 1960s. A trendline analysis since the 1960s would be interesting to see, and I hope someone puts it together. The challenge will be the ever changing methodology of the Census Bureau in calculating and categorizing the various groups.
The Hispanic Question, or Are Hispanics "White"
If you've seen recent data stating that America is currently about 77% white, and are wondering why this site is saying that America is actually 69% Caucasian as of 2000 (67% by 2004), well both are correct. Amazingly the Census Bureau counts all Hispanics that are not specifically black or Asian as white. I think this is a bit silly, since 99% of the time they are closer to the American Indian category (just not North American). I guess that since they aren't really native North Americans the Census Bureau didn't want to add them to that category. Or maybe it is all a conspiracy theory and they are trying to hide this major demographic shift from the public! Anyway, to get to the real numbers you need to look at the "Non-Hispanic White" category in the census data.