Older Southern American English is a diverse set of English dialects of the Southern United States spoken most widely during the mid-19th century, gradually transforming among its White speakers—possibly first due to economy-driven migrations following the American Civil War—up until the mid-20th century. By then, these local dialects had largely consolidated into, or been replaced by, a more regionally unified Southern American English. Meanwhile, among Black Southerners, these dialects transformed into a fairly stable African-American Vernacular English, now spoken nationwide among Black people. Certain features unique to older Southern U.S. English persist today, like non-rhoticity, though typically only among Black speakers or among very localized White speakers.

This group of American English dialects evolved over two hundred years from the older varieties of British English primarily spoken by those who initially settled the area. Given that language is an entity that is constantly changing, the English varieties of the colonists were quite different from any variety of English spoken today. In the early 1600s, the initial English-speaking settlers of the Tidewater area of Virginia, the first permanent English colony in North America, spoke a variety of Early Modern English, which itself was diverse. The older Southern dialects thus originated in varying degrees from a mix of the speech of these and later immigrants from many different regions of the British Isles who moved to the American South in the 17th and 18th centuries, as well as perhaps the English, creole, and post-creole speech of African and African-American slaves.

One theory of historian David Hackett Fischer's book Albion's Seed is that indentured servants chiefly from England's South and Midlands primarily settled the Tidewater (Virginia) region and poor Northern English and Ulster Scots families primarily settled the Appalachian Southern backcountry, so that the Tidewater and backcountry dialects were most directly influenced by those two immigrant populations, respectively. Indeed, the Appalachian dialect shows such likely immigrant influences as evidenced by, for example, their consistent preservation of rhoticity. However, linguists have disputed many of the specifics of Fischer's theory, instead arguing that dialect-mixing in both regions was in fact more varied and widespread. For example, an Appalachian Journal linguistic article reveals the flawed premises and misrepresentation of sources in Albion's Seed and asserts that the early Southern dialects are actually difficult to trace to any singular influence.

In the decades following the American Revolution of the 1760s to 1780s, major population centers of the coastal American South, such as Norfolk, Virginia, and Charleston, South Carolina, maintained strong commercial and cultural ties to southern England around London. Thus, as the upper-class standard dialect around London changed, some of its features were mirrored by: the dialects of upper-class Americans in eastern Virginia and the Charleston area, followed by the dialects of the surrounding regions in general, regardless of socioeconomic class. One such example accent feature is the "r-dropping" (or non-rhoticity) of the late 18th and early 19th century, resulting in the similar r-dropping found in these American areas during the cultural "Old South". Contrarily, in Southern areas away from the major coasts and plantations (like Appalachia), on certain isolated islands, and variously among lower-class White speakers, accents mostly remained rhotic. Another example feature is the British-style trap–bath split, which also helped define the eastern Virginia accent. The split was also adopted in the Gulf, Appalachian, and plantation regions of the South, though with their own articulation distinct from the British one. (The feature is extinct in virtually all these areas today.)

By the time of the American Civil War in the 1860s, many different Southern accents had developed, namely: eastern Virginia accents (including Tidewater accents), Lowcountry (or Charleston) accents, Appalachian accents, Plantation accents (those primarily of the Black Belt region), and accents in the secluded Pamlico and Chesapeake islands.

After the Civil War, the growth of timber, coal, railroad, steel, textile, and tobacco mill industries throughout the South, along with the whole country's resulting migration changes, likely contributed to the expansion of a more unified Southern accent (now associated with the 20th century), which gradually ousted 19th-century Southern accents. The South's 19th-century linguistic prestige was rooted in the plantation areas and higher-class White people, including features such as non-rhoticity. However, by the mid-20th century, linguistic features originating from Texas, Appalachian towns, and lower-class White people—such as rhoticity—were suddenly expanding throughout all the Southern States.

Also, before World War II, the demographic tendency of the South was out-migration, but after the war a counter-tendency emerged in the Southern cities, which received masses of migrant workers from the North: another possible motivation for the abandonment of older Southern accent features. Finally, the Civil Rights Movement seems to have led White and Black Southerners alike to resist accent features associated with the other racial group and even develop newly distinguishing features, which may have further contributed to the sudden mid-20th-century adoption of rhoticity among White Southerners of all classes, despite continuing non-rhoticity among Black Americans. Today, this linguistic divide on the basis of rhoticity, alongside other accent features, largely persists between Black versus White Southerners.

The phonologies of early Southern English in the United States were diverse. The following pronunciation features were very generally characteristic of the older Southern region as a whole: