 The population of the forty-eight counties of northern California has shown a steady increase over the years.The 1850 census almost certainly undercounted the population of the area, especially undercounting a still substantial Native American population.The largest percentage increase outside the Gold Rush era (51%) came in the decade of the 1940s, as the area was the destination of many post-War veterans and their families, attracted by the greatly expanding industrial base and (often) by their time stationed in northern California during World War II.