As of Wednesday, 56% of people who tested positive for COVID-19 were between the ages of 18 to 49, according to the California Department of Public Health.
The figures highlight a new trend in the impact of the virus that is widely considered to have the greatest effect on the elderly population. In comparison, those over the age of 65 who have been positively diagnosed now make up less than 15 percent of confirmed cases throughout the state.
The surge in cases among younger Californians has been partly attributed to an increase in testing and changes in criteria for testing, but officials have maintained that the younger population has a great impact on the spread of the virus.
On a local level, several of the state's counties are seeing similar trends among the younger population.
According to data from the Orange County Health Care Agency, 52% percent of cases are in individuals who are 44-years-old and below.
In neighboring Los Angeles County, nearly 40% of positive cases have been identified in individuals between 18 to 40 years old.
The county is among several throughout California that are being monitored for worsening coronavirus trends, including a rise in hospitalization numbers and an increase in the positivity rate as more businesses reopen.
L.A. County's health director warns if people and businesses don't follow safety orders, it could slow or even reverse the move to reopen the economy.
Gov. Gavin Newsom has also expressed increasing concern over these figures, as well as an increase in hospitalizations across the state, urging Californians to continue practicing physical distancing and to heed the statewide mandate on face masks.
On Thursday, the governor announced that California reported a 32% increase in COVID-19 hospitalizations over the past two weeks.
The virus is spreading at private gatherings in homes, and more young people are testing positive, Newsom said Wednesday.
"There is a sense that a lot of young people, well you're young so you feel a little bit more invincible but, respectfully, often that can be a selfish mindset," Newsom said.
Even if younger people may not show as many symptoms, they are still spreaders of the virus.
"And they can spread it to people that simply cannot handle the virus as younger healthier people can," he said.
The governor's warning fits with those made by city and state leaders in other parts of the US -- including across the South -- who have said an increasing number of young people are testing positive.
Some officials across the country have pointed to parties, bars and other gatherings as where that spread is happening.
The state reported large increases in testing this week and even broke a record Tuesday with an increase of more than 7,000 cases in a day, obliterating a record hit a day earlier, when more than 5,000 new cases were recorded.
CNNWire contributed to this report.