Madelyn is the American variant spelling of Madeline / Madeleine — from the Hebrew place name Magdala (the Galilean hometown of Mary Magdalene). Madelyn Hammond — Sweet Magnolias on Netflix. Madelyn Lynn — Insidious film series character. Madelyn Knight is the doll name of one of the American Girl historical figures (the 1944 character).
Madelyn 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 Madelyn reduce to 2, The Peacemaker. This is a traditional interpretive system, not a factual claim about the name.