California's department of Finance estimated California's population at 39.256 million on Jan 2016
California was estimating that the state population would exceed 40 million in late 2018 or early 2019.
Others like World Population Review have a slightly higher estimate.
California could hit a population of 60 million in 2050
Texas is projected to hit a population of 55 million in 2050.
US population could be nearly 350 million in 2025.
The US census tries to count illegals. The census takers will try to count everyone they see when they perform a statistical sampling. They make an attempt to intensively canvas some areas to get a better count. Then they subtract all known legal citizens and the remainder should be the illegals. But clearly illegals would tend to avoid census takers. So the US census estimates that they miss about 2% of regular people and 6% of illegals.
Some believe that the US census undercounts by more.
The US Census has been estimating about 11-12 million illegals for nearly two decades. Ann Coulter is famous for estimating that there are 30 million illegals. Over 20% of illegals are estimated to be in California. If the 30 million illegals in the US estimate were correct then California would have about 8 million illegals. This would mean California would be about 18% were illegal and not 6%.
Pew Research has an estimate of illegals by state