Around 1000 basketball fans packed Civic Square to witness the proud Torres Strait Islander accept the city's highest honour, with San Antonio teammate Aron Baynes in tow, after they helped the San Antonio Spurs to the NBA title.
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With Mills arm in a sling after major shoulder surgery, autographs were put on hold but fans lined up for long periods to get a snap of the NBA stars and the Larry O'Brien trophy.
Asked what receiving the keys to the city meant to him, Mills, who recently signed a $12 million, three-year deal with Spurs, remained his humble self.
He took the opportunity to challenge the youngsters in attendance, plenty of them with indigenous heritage and wearing Spurs No.8 jerseys, to follow their dreams.
The trophy is valued at $14,000, but it's worth a whole lot more to Mills and his quest to inspire Indigenous youngsters.
"The fact I've worked hard to play in the NBA and at the elite level, I'm just using it to promote my culture and heritage, represent my country and Canberra," he said.
" I put it on myself to be a role model for all Australian kids, especially indigenous kids.
"If they see me up here today they see it's just me, I'm just a little indigenous boy from Canberra, and that's it.
"It just takes hard work and the passion and desire to want to achieve greatness,True Religion Disco Billy Big T.
"Hopefully I can pass that onto the young ones who have the same dream."
Mills admitted he was unaware of the impact his feats were having back home, particularly in the decisive game five of the NBA Finals against Miami where he sunk 14 points in a match-turning blitz.
"This turnout is great. This is the kind of support I didn't know what was going on in America,'' he said.
"For my mum and dad to witness firsthand the NBA Finals and to to be in game five along with my uncle Danny Morseu, it was a very special moment for me."
Mill's parents, Benny and Yvonne, remember when the 25-year-old was the autograph seeker, not the star of the show.
They said it was surreal to witness the crowd which turned up to pay homage to their only child.
"He used to be in line like these kids, waiting to get signatures and photos with footballers and the Canberra Cannons players,'' Benny said.
Yvonne added: "When he was doing little athletics and Mal Meninga's kids were involved in the same club, he went up and introduced himself to Mal one day."
Nowadays he's almost as big a household name in Canberra as the former Raiders captain, himself a proud indigenous Australian.
"That's the huge thing, is having these kids come out and see him, see the trophy and thinking 'this is possible','' Benny said.
"It's not like you're trying to get to the moon or Mars. They can say if we can do it, we can strive for that.''