As of my knowledge cutoff in September 2021, the club with the highest number of clean sheets in a single English Premier League (EPL) season is Chelsea FC. Chelsea achieved this feat during the 2004-2005 season under the management of José Mourinho, their first season under his leadership.
During that season, Chelsea kept an astonishing 25 clean sheets in their 38 league matches, which is the highest number of clean sheets recorded by any team in a single EPL campaign. The defensive solidity and organization of Chelsea's backline, combined with the excellent goalkeeping performances of Petr Čech, played a significant role in this remarkable achievement.
Under Mourinho's guidance, Chelsea displayed an exceptional defensive record throughout the season. They conceded just 15 goals in total, averaging less than a goal every two matches. This defensive prowess formed the foundation of their successful campaign as they comfortably clinched the Premier League title, finishing 12 points clear of second-placed Arsenal.
The 2004-2005 season marked the beginning of a successful period for Chelsea, with the team known for its strong defensive organization and Mourinho's emphasis on disciplined play. The defensive record set that season showcased their ability to shut out opponents and demonstrated the effectiveness of their tactical approach.
It is important to note that records can be broken in subsequent seasons as teams continue to strive for excellence. Therefore, it is advisable to consult updated sources to obtain the most recent information on this topic.
Chelsea's achievement of keeping 25 clean sheets in a single EPL season stands as a testament to their defensive prowess and serves as a milestone in the league's history, highlighting the importance of a solid defense in achieving success.