Williams beat Larsson, the No. 8 seed and a local favorite, 6-4, 6-1 while winning nearly 60 percent of the points in the match. Williams dropped her serve twice in the first set but didn't face a break point in the second. She took 17-of-24 (70 percent) points on serve in the second set.
Her seven titles this year include the French Open.
By going 5-0 this week, Williams is 51-3 on the year.
The $40,000 first-place check pushed her career winnings to more than $46.6 million.
Larsson is 0-3 in WTA finals, having lost at Slovenia in July 2010 and at the Swedish Open in July 2011. She earned $20,000 as tournament runner-up, giving her a lifetime total of more than $950,000.