Silje was very popular in Norway in the 1980s and '90s. It ranked at #10 in 1980, #1 in 1985, #4 in 1990 and 1995 (behind Ida, Karoline and Marte both years), and was out of the top 10 by 2000.
One bearer of this name is a female character in the Norwegian book series, "The Tale About The Ice People". And another famous bearer is the Norwegian jazz singer, Silje Nergaard.