Here are California counties’ population growths in the last 120 years.
Early 20th Century
In the Roaring Twenties, the beginning of the transcontinental US Highways especially Route 66, increased population growth.
Later, even during the Great Depression, California’s population continued to grow. Dust Bowl refugees from states like Oklahoma settled in California.
Increased demand for defense and agricultural labor in the 1940s brought ever more people to California from elsewhere. Afterwards, many decided to stay because they liked the pleasant weather.
Mid 20th Century
California’s rapid growth continued after World War II. The growth in the defense industry in the early Cold War along with manufacturing, entertainment, and technology, contributed. Afterwards, to accommodate the massive numbers of newcomers, California underwent massive building of housing, schools, and roads.
The 1970 Census is the first census in which California is the most populous state. California overtook New York in the 1960s.
Late 20th Century
Growth in the aerospace and defense industries continued in the 1980s.Technology in Silicon Valley in the north also boomed. Stanford University encouraged its graduates to stay. Consequentially, this would also be the last growth spurt California would see.
In the 1990s California’s growth rate slowed dramatically amidst the end of the Cold War and a recession. Additionally, natural disasters such as the Northridge earthquake, Oakland Hills firestorm, as well as a major drought also occurred. The “California Exodus” started, even with the dot-com boom late in the decade.
Early 21st Century
Recessions at the beginning and end of the 2000s brought more financial troubles to California. The continued exodus accelerated by sky-high housing prices brought a net negative domestic migration. California gained no electoral votes in the 2010 Census.
California gained people in most of the 2010s from natural growth and immigration. In 2020 its population actually shrank. The state lost an electoral vote for the first time in the 2020 Census.
Maps
Here are the maps of the California counties’ population in the last 120 years.
