AUSTIN (KXAN) — Planet Earth just hit a new milestone.

The world’s population hit 8 billion Tuesday, according to estimates by the United Nations.

There are approximately 338 million Americans, accounting for approximately 4% of the world’s population.

Texas made up around 9% of the total U.S. population in the 2020 census, second to only California, and projections from the Texas Demographic Center show continued steady growth over the next few decades.

The center has two projections, depending on the rate of migration. If migration continues at the same rate seen from 2010 to 2020, Texas will surpass 40 million residents by 2049, and reach around 44.4 million in 2060.

If migration is slower, at half the rate seen between 2010 and 2020, the state’s population will reach 36.7 million in 2060.

The Texas Demographic Center says it recommends using the slower migration rate for long-term planning purposes.

When using those numbers, 10 counties are projected to have 1 million residents by 2060.

Harris County, home to Houston, will remain the most populous county by far, followed by Dallas, Bexar, Tarrant, Travis and Collin counties, all of which already have more than 1 million residents.

Denton County’s population is projected to hit 1 million in 2027, followed by Fort Bend County in 2035, Hidalgo County in 2041 and Williamson County in 2058.

If the higher migration rates continue, Montgomery and Hays counties could also have more than 1 million residents by 2060.

In both scenarios, Hays County is the fastest-growing in the state, reflecting patterns seen in recent years. Using the slower migration rate, the county’s population is expected to grow by 115% by 2060, making it the only county in the state to more than double its population by then. If the faster migration rate pans out, the county’s population would more than quadruple by 2060.

Sixteen other counties are projected to have population growth above 50% in the slower migration rate scenario, including Comal, Kaufman, Williamson, Fort Bend, Montgomery, Denton and Collin counties.

Meanwhile, 142 counties are projected to see population loss in this scenario, most notably Jeff Davis County, which could see its population decline by 65%.

In terms of raw numbers, Wichita County stands to lose the most people, with a population decline of more than 9,300 between 2020 and 2060.

Projections in the KXAN viewing area

As of the 2020 census, the population of the 15-county KXAN viewing area was just under 2.5 million.

Under the slower migration model, the population is projected to hit 3 million by 2035, and 3.7 million in 2060. In the faster migration scenario, the population could be approaching 5.5 million by 2060.

When using the slower migration scenario, the Austin metro counties — Bastrop, Caldwell, Hays, Travis and Williamson — are expected to add 1.2 million residents by 2060.

Meanwhile, most other counties in the region are projected to lose population, most notably San Saba County, which could see its population decline by 17% by 2060.