Jill is the English diminutive of Gillian — itself from the Latin Iuliana (feminine of Julius, "youthful, of Jupiter"). Jill Scott (born 1972) — American Grammy-winning soul singer; Who Is Jill Scott? (2000).
Jill 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.
In Pythagorean numerology the letters of Jill reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.