The all-time best single season record belongs to the Cincinnati Red Stockings, who posted baseball's only perfect record at 67-0 (57-0 against National Association of Base Ball Players clubs) in 1869. Their record would stretch to 81-0 across the 1870 season before losing 8-7 in eleven innings to the Brooklyn Atlantics in Brooklyn on June 14.

What's the best answer to this question: has any baseball team had a perfect season?
yes