Robert Koch married Emmy Fraatz. Together they had one daughter, Gertrud Koch.

Robert Koch divorced Emmy Fraatz. The reasons for the divorce are not widely documented, but his demanding career likely played a role.

Shortly after his divorce, Koch married Hedwig Freiberg, a young artist nearly thirty years his junior. This marriage seems to have been a source of personal happiness for Koch in his later years.

While details about his personal relationship with his daughter are scarce, it is known that Gertrud Koch was his only child from his first marriage. There is no public record of any children born out of the second marriage.