Ilona is the Hungarian form of Helen — from the Greek helios (sun), meaning "bright one." In Hungarian folklore, Tündér Ilona is the queen of fairies.
Ilona is widely used in Hungary.
Ilona 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 Ilona reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.