Allen joked last week that he didn't want to know how far away he was from the century mark and was instead just focused on playing his game.
But Chargers Head Coach Jim Harbaugh made sure to credit the 13-year veteran for his consistency and longevity in the league.
"It's awesome watching him do Keenan Allen things," Harbaugh said. "He is just one of the best and it's just great to be a part of [the milestone].
"I love being a part of it. I love watching it," Harbaugh added. "Justin to Keenan … it's just professional."
By hitting the 1,000-catch mark, Allen now has 930 career receptions with the Chargers. He can now set his sights on Antonio Gates' franchise record of 955 catches.