The London Knights picked Perry in the 1st round, 5th overall in the 2001 Ontario Hockey League draft. Perry played his first OHL game on September 16, 2001 vs. the Sarnia Sting. In his debut he notched his first OHL goal and first OHL assist. During Perry's Rookie season he scored his first OHL Hat Trick vs. Plymouth on February 15, 2002 on his way to winning OHL Rookie of the Month honours in February 2002. Perry finished 5th in OHL Rookie scoring with 59 points (28G, 31A) in his 60 games and was 3rd runner up in OHL Rookie of the year voting. Perry's Rookie season did however land him 2001-02 London Knights Rookie of the Year honours and he was named to the first all-rookie team. In the 2002 post season Perry managed 5 points (2G, 3A) in 12 games, he also tallied up 30 PIM.

Following his OHL All-star season the Mighty Ducks of Anaheim traded two second rounds picks for Dallas' 1st round choice to select Perry 28th overall in the 2003 NHL Entry draft to pick Corey Perry. Perry attended the Mighty Ducks 2003 training camp but was sent back for another season with the London Knights. In the 2003-04 season Corey Perry continued to show his ability. Perry was named OHL Player of the week for October 26, 2003, a week that saw him start a 19 game point scoring streak that lasted from October 23-December 19 2003 and saw him total 15 goals and 26 assists. In the middle of the streak Perry took part in the Canada/Russia challenge as a member of the OHL team as one of the top players in the League. Perry had an 8 game point streak that ran from December 27th 2003 to January 11th 2004, during which he netted 7 goals and 9 assists. Perry's strong season once again earned him an invitation to the OHL all-star game that took place in January of 2004. On February 22nd 2004, Corey Perry became the first London Knight to score 100 points in a season since Jason Allison did it 10 years prior during the 93-94 OHL Campaign. Perry scored at least a point in 58 of his 66 games during the 03-04 season with the London Knights notching 33 multipoint efforts along the way. Perry finished the season second in the OHL scoring race with 40 goals and 73 assists for 113 points. His 73 Assists topped the OHL. OHL coaches honoured Perry by voting him the 2nd smartest player in the league and the most dangerous in the goal area. Perry was named to the OHL first team All-Star Team and the top Right Winger in the OHL

Corey Perry's international hockey career began with a trip to the 2002 Under-17 World Championships as a part of Team Ontario where he won a Bronze Medal. Corey continued is Hockey Canada career being named to the 2002 Canadian National under-18 team for the Eight Nations Cup in Slovakia. Perry had 5 goals and 5 assists in Team Canada's gold medal winning effort. In 2003 Perry was invited to play on Team OHL in the Canada/Russia series. Following that he was invited to Team Canada's World Junior Championship tryout camp where he was one of the final cuts from the squad. Perry was once again invited to the Team Canada Junior tryout in 2004, this time making the team. Perry played on the top line with Sidney Crosby and Patrice Bergeron netting 2 goals and 4 assists in Canada's 5 games. Perry and Team Canada won the country's first gold medal since 1997.