It's a day that many of its students and staff were looking forward to for a while.
Though all the county's schools are now eligible to reopen, not all of them will do so right away. It is up to individual school districts to decide when and in what capacity to open.
"Being away from school has really been difficult for me, but I'm so excited to be back," said ASB President Kailia Utley.
Students brought the campus back to life Tuesday morning - many seeing each other, teachers and staff for the first time in months.
"It's just wonderful to see the cars coming in, but it's even more wonderful to see the smiles of the students behind the masks," said Principal Frances Clare.
Everything you need to know about reopening plans for LAUSD, OC schools
It was a similar scene at a number of schools across Orange County, like those in the Fountain Valley School District which reopened with a hybrid schedule this week.
In the Diocese of Orange, Catholic elementary schools returned earlier this month through the waiver process. Now middle and high schools are returning.
At Mater Dei, 25% of students will be on campus at one given time to allow for physical distancing, so classes have a maximum of 12 to 14 students. There's also a mask requirement, encouraged hygiene, and even a first aid tent with an isolation room, if needed.
"If setting it up like this lets us temporarily get back on campus, lets them get back to their senior years of high school, and back to whatever normal (is) gonna be, it's worth making the changes," said teacher Josh Dutra.
For legendary football coach Bruce Rollinson, it's one step closer to getting sports back to some type of normalcy.
"Four or five of my players walked by with great big smiles and I never thought I'd see them smiling about going to class! They've seen all the other helmet heads. Now they get to see all their friends," said Rollinson.
Bishop Kevin Vann even made an appearance to bless the campus and pray for protection.
"I've always liked new school years, but this is even more special because it follows a lot of apprehension and uncertainty, so here we are, we've arrived at this point," said Bishop Vann.
Mater Dei will continue at 25% capacity for two weeks. Next week, they'll resume extracurricular activities with the hopes of moving to 50% capacity the following week.
The return of students to Orange County schools comes as the county is within a week of possibly being moved up to the orange tier on the state's tracking COVID tracking system. That would mean more businesses would be given the green light reopen.