The eyes of the entire nation will soon be on President Obama’s Affordable Care Act, which takes full effect Jan. 1 with the requirement that nearly all Americans obtain health insurance or else pay a penalty on their taxes.

But many people probably don’t know that much of the new law has actually been in place for nearly three years now, and millions of Californians are already benefiting from its provisions.

Among the changes already here: an expanded public program for the poor; a high-risk insurance pool for people with pre-existing medical conditions; new benefits for seniors; and tougher insurance regulations. One of the most popular new rules was one of the first to take effect: requiring insurance companies to let adult children remain on their parents’ policies through age 26.

Jamie Tremmel, 23 and a student in her final year at UC Irvine school of law, is one of those affected. Without the change, she would have faced the uncertainty of finding insurance coverage on her own until she could find a job that offered it. Now that’s not a worry for at least three more years while she remains on her mother’s policy with Kaiser Permanente.

“It’s a relief,” Tremmel said in an interview. “Otherwise I might have had to go without insurance.”

While the provision that is helping Tremmel might be the best known, and possibly the most popular, of the Affordable Care Act’s early changes, some of the others are affecting more people.

A huge change has been the early expansion of coverage for low-income Californians. As part of what was known as the “Bridge to Reform,” the federal government paid for counties to expand eligibility to more than 700,000 people, mainly single adults with no children. In January these people and more will be part of an historic expansion of Medi-Cal. But many got their benefits early.

The head-start helped community clinics like those run by AltaMed in Orange County begin treating a population that until recently had no coverage and only episodic care. The network has been expanding its facilities and adding new services, including pharmacies to serve patients on site and staff to help them navigate the rules governing public assistance programs.

“A lot of people who haven’t had insurance are going to be getting coverage and seeking services,” said Mildred Pena, who oversees the operation of six Orange County clinics for Los Angeles-based AltaMed. “We want to be able to serve them.”

Some of the other changes in the health care system already in place include:

The state, using federal money, created a new high-risk insurance pool for people who could not get coverage because of pre-existing health conditions. About 16,000 people took advantage of the program. As of Jan. 1, the pool will no longer be needed because the law forces insurance companies to sell to all those who apply, regardless of their health condition.

Insurance companies have issued about $74 million in rebates to nearly 2 million California customers because of a provision in the law that requires them to spend at least 80 percent of their premium revenue on health care rather than administration, marketing and profits.

All newly sold insurance policies must now offer preventive care with no out-of-pocket cost to the consumer. Millions of Californians are benefiting from that provision, though it has likely been financed by a small increase in everyone’s monthly premiums.

Insurance companies can no longer cap the benefits a consumer can receive over his or her lifetime, a practice that used to mean that people with serious illnesses or accidents lost their coverage just when they needed it most. An estimated 12 million Californians are benefiting from that additional measure of financial security.

Seniors and people with disabilities on Medicare have received rebates and are seeing their prescription drug costs shrink thanks to a provision that closes what was known as the “donut hole” in their coverage. More than 300,000 Californians are benefiting from that change.

By design, Congress and President Obama front-loaded the parts of the law that were likely to be most popular with consumers (and voters) while delaying the least popular – mandates and new taxes – until at least 2014. Ironically, though, polls show that most people aren’t even aware of the perks they or their family or friends have already gained under the law.

“There’s so much talk about next year and all the things that will happen in 2014, that’s where the focus has been, but especially in California, we already have so much in place,” said Anthony Wright, executive director of Health Access California, which is tracking the implementation of health reform closely.

Daniel Weintraub has covered public policy in California for 25 years. He is editor of the California Health Report at www.calhealthreport.org