If you live in or have driven through Hays County, your eyes aren’t deceiving you. You’ve seen thousands of new residential rooftops pop up in the past decade.

In fact, Hays County ranks as the primary U.S. metro county with the most growth in new housing units (57.4 percent) from 2010 to 2020, according to U.S. Census Bureau data released November 2. Among those housing units are single-family homes, condos, townhomes, and apartments.

The number of housing units in Hays County rose by 34,117 from 2010 to 2020, the Census Bureau says.

One of the Austin metro area’s four other counties makes the top 10 on that list, too.

Williamson County saw the number of housing units shoot up by 46 percent from 2010 to 2020, the Census Bureau says. Among primary metro counties in the U.S., Williamson ranks fifth in that regard. Williamson County added 74,907 housing units during the 10-year period.

Three other Texas counties show up in the top 10 among primary metro counties:

• Third-ranked Comal County, part of the San Antonio metro area — 48.5 percent (22,831 new housing units).
• Seventh-ranked Fort Bend County, part of the Houston metro area — 41 percent (80,880 new housing units).
• 10th-ranked Rockwall County, part of the Dallas-Fort Worth metro area — 36.8 percent (10,280 new housing units).

The Austin metro area also claims one spot on the bureau’s list of the 10 “outlying” metro counties with the most growth in housing units from 2010 to 2020. The bureau defines outlying counties as those outside a region’s “urban center.”

Bastrop County, ranked eighth on that list, saw the number of housing units go up 25.1 percent from 2010 to 2020 with the addition of 7,367 units.

Four other Texas counties appear on the same list for “outlying” counties:

• No. 1 Denton County, part of the Dallas-Fort Worth metro area — 36 percent (92,136 new housing units).
• No. 2 Montgomery County, part of the Houston metro area — 34.2 percent (60,842 new housing units).
• No. 3 Kaufman County, part of the Dallas-Fort Worth metro area — 33.7 percent (12,906 new units).
• No. 5 Kendall County, part of the San Antonio metro area — 30.4 percent (4,275 new housing units).

“The number of occupied housing units grows when new housing is built or previously vacant homes become occupied. It decreases when housing units become vacant, are demolished or are converted into other uses,” the Census Bureau explains.