Mildreth is of Anglo-Saxon origin, derived from the Old English elements "mild" meaning gentle and "þrēoþ" signifying strength or power. The name was brought to England by the Saxons when they invaded Britain in the mid fifth century. Over time, it has evolved phonetically and orthographically into its current form. Although not as common today, Mildreth can still be found in some historical records and family lineages tracing back generations.
The name Mildreth experienced intermittent popularity throughout the 20th and early 21st centuries, with peak years being 1897, 1916, 2007, and 2008 where 7 or more babies were named Mildreth. However, it is clear that this name has become quite rare in recent times, as there were no births with the name Mildreth recorded after 2009. In total, over the period from 1897 to 2009, there were 61 babies born who were named Mildreth.