In the third inning of a 3-1 Yankee victory over the White Sox, Reggie Jackson connects off of Britt Burns for his 400th career home run. Mr. October will finish his 21-year career with 563 dingers, placing him sixth on the all-time list when he retired in 1987.

On August 11, 1980 — In the third inning of a 3-1 Yankee victory over the White Sox, Reggie Jackson connects off of Britt Burns for his 400th career home run. Mr. October will finish his 21-year career with 563 dingers, placing him sixth on the all-time list when he retired in 1987.

Source:
Baseball Reference August 11
National Pastime
Retro Sheet
Hall of Fame
SABR Games Project
Replay The Game