Courtly or dweller by the court
A modern American invention likely blending the surname Courtney with the popular 'lin' suffix. It suggests a sense of courtly refinement or can be interpreted as a topographical name referring to one who lives near a court or enclosed yard.
Less common today
Courtlin isn't in the latest US Top 1000. It last peaked at #7,140 in 1997.
US births per 5-year period, 1990βpresent (SSA data).