Williamson County Texas Population 2024. Williamson county, texas's estimated 2024 population is 722,109 with a growth rate of 3.57% in the past year according to the most recent united states census data. Williamson county, texas is the 12th largest county in texas.
Percentage of population (2018) white. The population of williamson county, texas in 2022 was 671,418, 57.4% up from the 426,568 who lived there in 2010.