Over the past 110 years, 53 069 boys have been named Rex. The name Rex ranks 426th in the United States among the most common names for boys. For the first time more than ten times newborns were named Rex in 1910. The peak of popularity of the name Rex came in the 1930s and 1950s. You can see absolute numbers and relative numbers on the chart. Indicators per 100K more accurately assess the popularity of the name.