It’s time for some fun with numbers, dissecting a new state report on population trends.

The big number is 39.8 million. That’s the state Department of Finance’s latest calculation of California’s population as of Jan. 1.

It’s doubtless a little low, since California has a very large number of residents who fly below the official radar – the homeless and many undocumented immigrants, particularly. So let’s call it 40 million.

That’s almost twice as many as those living in California when Jerry Brown began his first stint as governor in 1975. However, as the latest data again confirm, the state’s rate of population growth has been declining.

During the 1980s, thanks to high immigration and birth rates, California was expanding by 2-plus percent a year, adding 6 million residents in just 10 years. However, immigration, legal and illegal, is now a fraction of what it once was (we lose more people to other states than we gain) and births are declining while deaths are rising.

In 2017, the state report says, California added just 309,000 people. Numerically, that’s about half of the 1980s surge and our annual growth rate (.78 percent) is scarcely a third of what it was then.

Inland communities continued to grow faster than those along the coast last year. Merced, at 1.7 percent, was the state’s fastest growing county, while Sacramento, which reached 500,000 for the first time, was its fastest growing large city, in both cases thanks largely to migration from coastal regions in search of affordable housing. Speaking of which, the state’s report confirms anew that California is still falling far short in meeting its housing needs.

With the average California household at 2.8 people, the 309,000 Californians added last year needed about 110,000 new housing units, but the state’s net gain last year was just 85,000 units, according to the report. While new housing starts topped 100,000 during the year, losses to fire and old age dropped the net gain below demand.

The state housing agency estimates that California needs to build 180,000 units a year to meet current demand and deal with a very large backlog. California once was building that many units, but has never fully recovered from the Great Recession’s housing meltdown.

Raising production significantly would require difficult policy changes, such as streamlining environmental regulation and overcoming local anti-development pressure, but the state’s political leadership has so far failed to do what needs to be done.

Finally, the population numbers are a new indication that for the first time ever, California’s congressional delegation may shrink after the 2020 census.

There are 435 seats in the House of Representatives and after every census, they are reapportioned among the states, based on how their populations have changed during the preceding decade.

California’s growth rate is now very close to the nation’s and if the 2020 census confirms that trend, the state’s delegation, now 53 seats, could drop by one.

That’s why California’s politicians are strongly opposed to the Trump administration’s plans to add a citizenship question to 2020 census forms. They fear that California’s non-citizen residents, especially those in the country illegally, will shy away from being counted and an undercount will cost the state a congressional seat, as well as lower the flow of census-based federal funds to the state.

That’s why, too, the state is prepared to spend tens of millions of dollars to encourage its 40 million residents to be tallied.

Call it political numerology.

We want to hear from you

Want to submit a guest commentary or reaction to an article we wrote? You can find our submission guidelines here. Please contact CalMatters with any commentary questions:

Dan Walters has been a journalist for more than 60 years, spending all but a few of those years working for California newspapers. He began his professional career in 1960, at age 16, at the Humboldt Times...