The oldest recorded dictionary dates from the 3rd to 2nd millennia B.C. It is a set of cuneiform tablets from the Akkadian empire with word lists in Akkadian and Sumerian. The oldest monolingual English dictionary is Robert Cawdrey's "A Table Alphabeticall," published in 1604.
"A Table Alphabeticall" was unreliable. The first definitive English dictionary was Samuel Johnson's "A Dictionary of the English Language," published in 1755. Johnson's dictionary was the authoritative standard for the English language until the publication of the Oxford English Dictionary in 1884.
Noah Webster published the first American English dictionary in 1806. Webster believed in spelling reform and introduced new spellings with his dictionary, such as "color" instead of "colour." Webster's original dictionary accounts for many of the differences between American English and British English spelling rules.