The Census Bureau released population estimates Thursday that say California remains the nation's most populous state with 36.5 million residents, but figures from the state Department of Finance say there are 987,000 (37.5 million total) more people in July, 2006 than estimated by the Census Bureau. The difference is based on the federal government using IRS tax records to count who is a californian and the state using driver license records. Many people who are in california from another state would likely choose to claim out of state residency because california has a high tax rate.
California has an estimated population growth rate of 1.2 to 1.4% for 2007-2010.
This is detailed analysis of california population forecasts It discusses the undercounting in the 1990 and 2000 census. About 4.2% of children under the age of 4 were not counted. It also discusses the main issue that will greatly effect the forecasted population of california. How quickly will the birth rate of recent hispanic arrivals to California fall ? If it falls slowly then the birthrate in California would rise to 2.7 from about 2.26 now. The undercounts also underestimate the birthrate from 2.26 from 2.12. The other big issue is if California can continue over the long term to attract people from other states.
Undercounting illegal immigrants and children means that the current US census population clock could be undercounting by 2-3% for the entire United States. Plus the census forecasts would be using birthrates that are too low.
Lifespan estimates could also be overly pessimistic with breakthroughs against diseases like diabetes and aging in general. Also, more widespread use of fertility treatments could increase the number of births for older women.
California's population is probably
38 million (April 2007) instead of 36.9 million
by Dec 2010 the population will be 40 million.
I think the estimates for california are
2020 45 million +- 1 million
2030 50 million +- 1.5 million
2040 55 million +- 2 million (US census projects 46 million)
The US population is probably
307 million now (April 2007) instead of 301.5 million.
Dec 2010 318 million (census projects 310.7 million for July 2010
The high series estimate for the census bureau is in table C of this PDF from 1996 on page 5. It projects 295 million in 2005, 314 million in 2010, 357 million in 2020, 405 million in 2030, 458 million in 2040 and 519 million in 2050.
2020 352 million Census middle projection is 336.8 million or 335.8 million
2030 398 million (Census projects 363 million)
2040 450 million Census projects 392 million
2035 would have about 420 million, which is 113 million more than now with 5.5 million in missing undercount. The developed world would thus have far more than a total 40 million population increase.