Some is done overseas by "back office" companies in China, India, Ghana etc. Even in those where the indexing is done by the clerks certain documents are not allowed to be reproduced over the Internet or may not be available as they come from another government entity such as the civil  and probate courts which fall under different laws prescribing what is private and whose public accesses the records.

You might want to note as well that in many if not most counties whose records are online, the county no longer owns or controls the images or the indexes regardless of who entered them. Some of these companies are very good at posing as official sites. To learn who owns and controls the images, find the copyright notice.