Julianna is the feminine of Julian — itself from Julius, the Roman family name. The root meaning is likely "youthful" or "downy-bearded" (an epithet of Jupiter). Saint Juliana of Nicomedia (early 4th century) was an early Christian martyr.
Julianna has been climbing steadily in the U.S. since the 1990s. The actress Julianna Margulies (ER, The Good Wife) is a prominent bearer. Today the name sits in the U.S. top 200.
Julianna does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
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In Pythagorean numerology the letters of Julianna reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.