OED 1 defines it as “U.S. A yard or garden-patch about the door of a house” and offers the following citations:
c. 1764 in T. D. Woolsey in Hist. Disc. [...] The Freshmen ... are forbidden to wear their hats ... in the front door-yard of the President’s or Professor’s house. 1854 Lowell Cambr (Mass.) 30 Yrs. Ago [...] The flowers which decked his little door-yard. 1878 Emerson in N. Amer. Rev. [...] We send to England for shrubs, which grow as well in our own door-yards and cow-pastures. 1913 R. Frost Boy’s Will 9 How drifts are piled, Dooryards and roads ungraded. 1941 T. S. Eliot Dry Salvages [...] The rank ailanthus of the April dooryard.
I note that all of these except the Eliot are from Yankee sources; and although Eliot was born and raised in St. Louis, his parents were New Englanders.
However, probably the most famous use of the word is Walt Whitman’s elegy on Lincoln, When Lilacs Last in the the Door-yard Bloom’d—and Whitman lived his whole life on Long Island and in Camden, New Jersey, except for a brief period during and immediately after the Civil War.
A posting on rootweb.com, Some Old Houses in Readfield, Maine, describes the evolution of Maine architecture and provides detail about the origin of “door yard call”:
Over time [...] men could find time to make additions and improvements to the log cabins — sometimes the original cabin became an outbuilding, and a finer house was built. Sometimes the original cabin was enveloped, and a century later the unsuspecting eye would never have guessed that a log cabin was nestled inside a lovely Victorian structure. In the mid 19th century it became common in Maine to build a summer kitchen, shed and barn onto the house (usually a cape cod style house) creating a “big house, little house, back house, barn” effect. This architectural style caught on about the time of the mass exodus west, and at the beginning of the agricultural decline in Maine, thus our extended farm buildings are rarely seen in the rest of the USA. The disadvantage was, of course, threat of fire which would destroy the whole farm, and the smells and flies that went with an attached barn. Some of the advantages were easy accessibility to the barn, animals, food storage areas, milk room and sleigh in the winter; protection from the winter winds both outside and in, added warmth for the animals; and last but not least an indoor trek to the privy at the back of the barn or shed. If you mention a door yard in another part of the country chances are they will not know what you are referring to. With the extended farm buildings there were three yards: the front yard by the parlor where special guests were greeted, the barn yard where the men did their farm chores, and the door yard by the shed or summer kitchen where women did laundry, planted and tended their kitchen garden and did other woman's work. Sometimes we still hear the term “door yard call”, and now you know the origin — you wouldn't want to disturb someone for any length of time while they were working so you just stop for a moment on your way by for a quick hello in the yard — you made a “door yard call” .