Not found before the 1920s, and not common until the 1940s, but increasingly popular since, being borne, for example, by the American actress Cheryl Ladd (b. 1951). It appears to be a blend of Cherry and Beryl.
English (Yorkshire): 1. from Middle English swal(e)we, swalu ‘swallow’, hence a nickname for someone thought to resemble the bird, perhaps in swiftness and grace. 2. habitational name from a place in Lincolnshire, so called from the Swallow river on which it stands. The river name is probably ultimately akin to that of the bird, with some transferred meaning such as ‘swirling’ or ‘rushing’.