The name reached its all-time peak in 1999 with 3 births ranking #3900. STABLE Recent data shows the name is currently stable.
Finnley is a modern spelling form of the Finley family and is generally understood through the same "fair warrior" background. It keeps the familiar sound while making the opening element more visibly like Finn.
This spelling is modern and style-led rather than traditional in its own right. It belongs to the broader trend of refreshing older Celtic names through spelling tweaks.