USA's Heather O'Reilly (#9), one of the most-capped and most-decorated players in women's football history, announced her international retirement on September 1, 2016. (Photo: FIFA via Getty Images)

CHICAGO -- Heather O'Reilly, one of the most successful players in United States women's national team history, announced Thursday her retirement from international soccer.

The 31-year-old will close the curtain on her 15-year international career on September 15, when the U.S. hosts Thailand in an international friendly Columbus, Ohio.

"Heather has been a vitally important part of our program for many years and has continued to set a standard for professionalism and work ethic," said U.S. head coach Jill Ellis. "She's been right in the thick of things for most of our big moments over the past 15 years and has always been the ultimate team player and a world-class person. She should be incredibly proud of the indelible impact she's made on this team and on women's soccer."

O'Reilly, who will continue playing club soccer, began her career as one of the youngest players to debut for the USA over the past 15 years, playing her first international match on the senior level at 17-years-old during the Algarve Cup against Sweden on March 1, 2002.

She currently has 230 caps, the seventh most in U.S. women's history. Her 46 goals are good for 12th on the USA's all-time scoring list.

"I have spent nearly half my life in a U.S. Soccer uniform, so making the decision to retire from international play was incredibly hard and emotional," said O'Reilly. "But quite simply, after 230 caps, thousands of practices, many trips around the world, and having played in three World Cups, and three Olympics, it just feels like the right time.

“I've had an incredibly complete career playing for my country and it has been an absolute honor to represent the USWNT for the last 15 years. I'm leaving this team with a lot happiness in my heart and pride for what we've accomplished. I truly love this game and it will be in my life forever.”

O'Reilly finishes as one of just four three-time women's soccer Olympic gold medalists and a 2015 Women's World Cup champion. She was also a leader on the U.S. team that won the 2002 FIFA Under-19 Women's World Cup, making her one of the few players in history to win an Olympics, a senior World Cup and a youth World Cup.

O'Reilly retires having played in three Women's World Cup tournaments (2007, 2011, 2015) and likely would have been on the USA's 2003 Women's World Cup Team as well were it not for a broken leg suffered against Ireland in June of that year. She played in three Olympic Games, winning three gold medals (2004, 2008, 2012).

O'Reilly began her professional club career with Sky Blue FC in WPS, playing there from 2009-11 and helping the team to the league title in 2009, scoring the game-winner in the championship game en route to being named the championship game MVP. She played with the Boston Breakers in the WPSL and NWSL from 2012-14 before joining FC Kansas City for the 2015 season where she helped the club to the league title, assisting on Amy Rodriguez' match-winner.