Koskie was drafted by the Minnesota Twins in the 26th round of the 1994 amateur draft, and subsequently made his Major League debut on September 9, 1998. He established himself in 1999 as the Twins' third baseman of the future by hitting .310 and knocking in 58 runs. In 2000 he batted .300 with a .400 on-base percentage and in 2001 he had his most offensively productive season when he hit 26 home runs, had 103 RBIs, and scored 100 runs.
Koskie signed a three-year, $17.5-million deal with the Toronto Blue Jays on December 14, 2004. An injury-plagued 2005 cut his productivity and playing time, as he struggled with a .249 average, with 11 home runs, 36 RBIs, and 4 stolen bases in 97 games. Despite his frequent injuries, Koskie was regarded as one of the more athletic third basemen in the game.
On January 6, 2006, he was traded by the Blue Jays to the Milwaukee Brewers for minor-league pitcher Brian Wolfe. The deal was widely viewed as a salary dump for the Blue Jays, who had also created a logjam at third base when they traded for Troy Glaus. With several players on the roster at that time capable of playing third base (Koskie, Glaus, Eric Hinske, Shea Hillenbrand, and Aaron Hill) and no assurances of regular playing time from Blue Jays GM J.P. Ricciardi, Koskie was traded just a year after being the Blue Jays' 2004 offseason marquee free agent signing. When the Brewers acquired Koskie, he had $11.6 in guaranteed money remaining on his contract. His salary was $5.25 million in '06, and $5.85 million in '07. The Brewers paid $2 million each season, with the Blue Jays paying $3.25 million in '06 and $3.85 million in '07.
While the Brewers acquired a veteran infielder with a solid glove and bat to anchor their very young infield, Koskie's later seasons were marred by injuries, including missing most of the 2006 season with post-concussion syndrome. He hit .261 with 12 homers and 33 RBI in his half-season with the Brewers in 2006. He suffered the injury in a fall while chasing a popup on July 5, 2006, in a game against the Cincinnati Reds.
Still dealing with postconcussion syndrome, Corey Koskie reiterated in mid-June 2007 that he wasn't certain whether he would play baseball again. "If I can't play, I at least want my life back," he said. "I'm hoping to do something to help the team this year. I want to play baseball again. If I can play baseball, I know I'm fine."
The injury caused him to miss the entire 2007 season.  Koskie was in town for the last weekend of the regular season and reported that he began making progress in his recovery around the beginning of September after starting to work with a new therapist.
The Brewers in October 2007 declined to pick up the 2008 option for Koskie. The agreement stipulated that the teams would split the $500,000 buyout, so the Brewers will pay $250,000 for declining the 2008 option. The arrival of Ryan Braun in 2007 made it all but a done deal that Koskie would not be with the Brewers in 2008, even if he completely recovered from the symptoms of his post-concussion syndrome.
|Topps Rookie All-Star Third Baseman|