Variant of Darlene, from Old English 'deorling' meaning darling or beloved one.
Darleen is a characteristically American name, born in the early twentieth century from the creative energy that was producing a new feminine naming culture largely independent of European precedent. The base word is darling — the English term of endearment from the Old English dēorling, "little dear one," itself from dēor (dear, beloved) — to which the productive suffix -een or -ene was appended, following the pattern of names like Charlene, Marlene, and Pauline. The result is a name that is essentially a term of endearment formalized: to name a child Darleen is to freeze a mother's or father's feeling about her into permanent form.
The name rose to popularity through the 1940s and 1950s, reaching its peak in the years immediately following World War II when American popular culture was producing a wave of invented or lightly adapted feminine names. It had particular strength in the American South and Midwest. The variant Darlene (one e) was slightly more common, but Darleen with its distinctive double-e has a softer visual quality and was favored in communities that wanted a small orthographic individuality.
The name appears in the era's fiction, film, and television as a marker of middle-American femininity — warm, cheerful, unpretentious. By the 1980s, Darleen had begun its generational descent, becoming a name most associated with the mothers and grandmothers of younger children rather than the children themselves. This cycle, as with all mid-century American invented names, is now reversing at its edges — names like this are beginning to acquire the patina of genuine vintage, poised eventually for rediscovery by the great-grandchildren of their first bearers.