The tournament is the 32-year-old’s last chance to win a Grand Slam in 2014, which starts on Monday.
The pair will learn their first-round opponents when the draw is made from 17:00 BST on Thursday.
French Open champion Maria Sharapova, who won the title at Flushing Meadows in 2006, is seeded fifth.
Victoria Azarenka, beaten in the past two US Open finals, is seeded 16th after an injury-hit year.
American five-time champion Williams is hoping to win her 18th Grand Slam title, equalling the feats of Chris Evert and Martina Navratilova.