Merriam-Webster Collegiate Dictionary - don't

 I. Date: 1639  1. do not  2. does not Usage:  Don't is the earliest attested contraction of does not and until about 1900 was the standard spoken form in the United States (it survived as spoken standard longer in British English). Dialect surveys find it more common in the speech of the less educated than in that of the educated; in those places (as the Midland and southern Atlantic seaboard regions) where it has lasted in educated speech, it is most common with older informants. Surveys of attitudes toward usage show it more widely disapproved in 1971 than it had been 40 years earlier. Its chief use in edited prose is in fiction for purposes of characterization. It is sometimes used consciously, like ain't, to gain an informal effect.  II. noun  Date: 1894 a command or entreaty not to do something a list of dos and ~s