Based on its geographic size, Rockwall County is the smallest county in Texas, at just 149 square miles. But don’t let its size fool you when it comes to wealth. Rockwall County also is the richest county in the state.

Data analysis website Stacker compiled a list of the wealthiest counties in Texas based on median household income, and Rockwall County came out on top at $100,920. It was the only county in Texas to break the $100,000 mark.

Among all U.S. counties, Rockwall County ranked 32nd for the highest median household income, according to Stacker.

The continuing influx of people into Rockwall County is helping drive up the median household income.

Rockwall County was home to more than 116,000 residents in 2021. From 2020 to 2021 alone, the county’s population grew 7.94 percent, making it the state’s third-fastest-growing county during that period. Some of the population boom stems from East and West coast transplants fleeing higher-priced locales.

Additionally, residents of Rockwall County are highly educated, which contributes to their earning power. As of 2020, 93 percent of the county’s residents 16 and over had graduated from high school, and nearly 43 percent of residents 25 and over had earned at least a bachelor’s degree. Both of those figures are well above the statewide numbers.

There’s also the livability factor. Rockwall, the biggest city in Rockwall County, ranked fourth on Money magazine’s 2020 list of the best places to live in the U.S. — which almost certainly adds to the county’s allure for high-income households.

“Rockwall is only 25 miles outside [the] Dallas city limits. For us, it’s a good balance of small-town life, great schools, and reasonable access to a world-class city when we need a little more hustle and bustle,” Dallas Moms blogger Gabrielle Cullen wrote in 2017.

To come up with its list, Stacker used U.S. Census Bureau data from 2019 showing the five-year estimate for median household income in each of Texas’ 254 counties. Aside from Rockwall County, nine other counties in Dallas-Fort Worth made Stacker’s list of the 50 richest counties in Texas. The other counties, followed by their median household income, are:

• No. 3 Collin County, $96,913
• No. 6 Denton County, $86,913
• No. 14 Parker County, $77,503
• No. 15 Ellis County, $76,871
• No. 26 Kaufman County, $70,107
• No. 31 Tarrant County, $67,700
• No. 38 Wise County, $64,536
• No. 39 Johnson County, $64,359
• No. 40 Hood County, $64,041

By comparison, the median household income for all of the U.S. was $68,703.

Among the state’s four major metro areas, DFW dominated in terms of the number of rich counties in Texas’ top 50. It’s worth noting, though, that DFW has more counties (11) than any other metro in Texas.

Here’s how the state’s three other major metros fared in the Stacker rankings for highest median household income by county.

Austin

• No. 5 Williamson County, $87,337
• No. 18 Travis County, $75,887
• No. 29 Hays County, $68,717
• No. 36 Bastrop County, $64,597

Houston

• No. 2 Fort Bend County, $97,743
• No. 4 Chambers County, $91,141
• No. 9 Brazoria County, $81,447
• No. 10 Montgomery County, $80,902
• No. 22 Galveston County, $73,330
• No. 34 Austin County, $66,206
• No. 48 Harris County, $61,705

San Antonio

• No. 7 Kendall County, $84,747
• No. 11 Comal County, $79,936
• No. 16 Wilson County, $76,692
• No. 21 Guadalupe County, $74,496
• No. 46 Medina County, $62,599