"She was my No. 1 fan," said Maguire, who transferred to St. Mary's from St. John's two years ago. "She didn't miss a game. She supported the team in general. She was always at team dinners. She supported me playing football and my transfer to St. Mary's. She played a big role."
Maguire found himself turning to football to help get his mind away from the pain of his mother's death. Offseason workouts with his teammates kept Maguire's schedule busy and helped him cope with the loss.
"It was a good distraction," said Maguire, a Nahant native. "I was always busy with practice, things like that. All the coaches were helpful. It just made it easier.
"I couldn't imagine playing with any other group of guys and getting through the year with anybody else."
Now, after a season that started in the worst way possible, Maguire's one win away from sealing his St. Mary's career with a state championship. The Spartans will play Blackstone Valley Saturday morning (11) at Gillette Stadium in the Division 7 Super Bowl.
"It's definitely been a ride," Maguire said. "There's been a lot of ups and downs. I think my teammates understand how important this game is to me. I'm playing this season and dedicating it to my mom. They understand that and it's meant a lot to me. Football has definitely helped."
First-year St. Mary's coach Sean Driscoll, who was hired during the offseason, was just a few months into his new role when Terri died. Driscoll was still getting to know Maguire but it didn't take him long to come away impressed with his resiliency.
"What I learned about Jack is his resiliency in bouncing back from something like that," Driscoll said. "I know he has a younger sister (Riley) at home and he helped her. He helped manage things with his dad (Kevin) and his brother (Owen). They're a solid family.
"I really noticed Jack's leadership. I told him he could take some time off. I think he felt the distraction was good for him. I've been coaching for 26 years now and there are very few who could have dealt with it the way he's dealt with it."
Maguire's younger brother, Owen, brought a banner to Tremont Street earlier this year with St. Mary's golf team. Owen worked his through a bunker on his final hole in the Division 3 state championship, proving crucial in a one-shot win over Dover-Sherborn. Owen is a junior at St. Mary's and Riley's a sixth-grader.
The Spartans will face a formidable Blackstone Valley team (10-1) that hasn't lost since its season opener. The Beavers lost to Mashpee in last year's Super Bowl, the same team that ended St. Mary's 2017 season in the state semifinal.
"They're a good team," Maguire said of the Beavers. "They're playing in the state championship game. It'll be a good battle. They're pretty good up front. They run the ball well. We just have to play our football, go out there and play our game."
A win Saturday, Maguire said, would be the ideal ending to a season that has taught him more than he'd imagined.
"It'd mean everything," Maguire said. "There's nothing better than winning the state championship as a senior. There's nothing better. To me personally, I know this would be really important to my family, all my close friends and all those who've supported me throughout the year."
Although his mother won't be at Gillette Saturday, Maguire's confident she'd be proud of what he's helped the Spartans accomplish this season.
"It added a lot of emphasis to this season," Maguire said. "It helped me realize how important this is. Regardless of what happens I know she'd be proud of me."