Klāvs Siliņš: Latviešu personvārdu vārdnīca. Riga "Zinātne" 1990, ISBN 5-7966-0278-0
Population Register of Latvia: Kirils was the only given name of 1767 persons in Latvia on January 1st 2011, including Russian speakers.
Etymology
First recorded as a given name of Latvians in the 18th century. From RussianКири́лл(Kiríll), ultimately from Ancient Greek. Cognate with English Cyril.