September 26, 1960 -
Ted Williams last at bat is his 521st home run.
"He is the last player in Major League Baseball to bat over .400 in a single season (.406 in 1941). Williams holds the highest career batting average of anyone with 500 or more home runs. His career year was 1941, when he hit .406 with 37 HR, 120 RBI, and 135 runs scored."
Source: Wikipedia