In 1831, George and Charles Merriam founded the company as G & C Merriam Co. in Springfield, Massachusetts. In 1843, after Noah Webster died, the company acquired the rights after the death of Noah Webster in 1843 to his An American Dictionary of the English Language. This work had first been published in 1828 and was the first American unabridged dictionary. A second edition had been published in 1840, and subsequent editions were published by the company in 1847 and 1864. The 1890 revision was given the title Webster’s International Dictionary and was followed in 1909 by Webster’s New International Dictionary, Second Edition, and in 1961 by Webster’s Third New International Dictionary.
Merriam-Webster dictionaries began to be published in electronic formats, including CD-ROMs and handheld devices, in the 1980s. In 1996 Merriam-Webster introduced Merriam-Webster OnLine, a Web site offering language-related features, including access to the full text of Merriam-Webster’s Collegiate Dictionary and Merriam-Webster’s Collegiate Thesaurus. In 2002 Webster’s Third New International Dictionary was made available online at a subscription Web site.
In 1964, Encyclopædia Britannica, Inc., acquired Merriam-Webster, Inc., as a subsidiary. The company adopted its current name in 1982.
Among the dictionaries are Webster’s Third New International Dictionary of the English Language (1961), which contains more than 476,000 entries and provides the most extensive record of American English now available, and the 11th edition of Merriam-Webster’s Collegiate Dictionary (2003).
According to britannica.com