The Dōngběi dialects comprise a Mandarin subgroup that is related to, but nevertheless clearly distinct from, the Běijīng dialect. The dialects are an exceedingly young variety formed by a huge wave of emigrants from northern Chinese provinces who moved into the theretofore sparsely populated Manchurian territory in the late 19th and early 20th centuries. The new immigrants were primarily from Shāndōng and Héběi and they came in numbers that overwhelmed the languages spoken by the previous inhabitants, comingling with each other, then developing into a new set of regional varieties of Mandarin. This paper first examines the history of the population in China’s northeast and its growth from the beginning of the Qīng dynasty in the mid 17th century to its peak in the 20th, paying particular attention to the origins of the large Chinese speaking migration into the region at the end of the dynasty. Following, this study looks at the phonology and lexicon of the new regional varieties — the northeastern Mandarin dialects, investigating their characteristics and classification to show that historical and geographic factors have resulted in discernable differences between the Dōngběi and Běijīng dialects, differences that are sufficient to warrant separate classification.