The singer sold 76,000 copies of the record to achieve a 12th week at the top of the chart, making it the most weeks at number one for an album since Santana's Supernatural in late 1999 and early 2000.
21 hasn't left the top three of the Billboard 200 since it debuted at number one 24 weeks ago. It was recently certified triple platinum in the US having sold around 3 million copies, making it the biggest-selling album of the year so far.
Elsewhere on the chart, last week's number one - Eric Church's Chief - slips to two, Trace Adkins is at number three with Proud to Be Here and Mat Kearney sits at number four with Young Love. The soundtrack to the Nickelodeon TV series Victorious completes the top five.
Meanwhile, Amy Winehouse, who re-entered the Billboard 200 following her death, falls from seven to 16 with Back to Black. Her debut Frank also slides from number 33 to 58.
21 was recently named the biggest-selling digital album to date in the US.
Watch Adele's video for 'Rolling In The Deep' below: