When it comes to population growth in the Waco area, we can no longer use the past to predict the future. The population trend line reflects a long pattern of slow, steady growth in Waco and McLennan County with no immediate change in sight. If projections hold true to form, the population of the county will increase 10 percent to 15 percent between the 2010 and 2020 Census dates, much like it’s done since 1970. Waco’s virtually landlocked population will also increase, although at a slower rate.

Forget true to form. Waco is in the bulls-eye of population growth and, despite current projections, growth in McLennan County is about to hit a new gear.

Between 2000 and 2010, Waco’s population grew 8.59 percent. McLennan County grew 10.02 percent. That certainly holds with historical data for the county, which grew 12 percent in the 1990s, 10 percent in the 1980s and 14 percent in the 1970s. As of July 1, 2013, the McLennan County population was 241,481, and 129,030 for Waco. Since the Census, there has been little change in the growth rate — 2.8 percent for the county and 1.8 percent for the city over three years. If anything, it appears to be slowing. Texas’ population has grown 5.2 percent since the Census. For a long time, local population growth rates have hovered around 1 percent annually.

To get a grasp of what’s to come, look to our north and to our south.

McLennan County sits halfway between two major cities — Austin and Dallas — whose suburbs populate virtually every “fastest-growing” list published since 1990. It also lies within the Central Texas Triangle, where 80 percent of Texans live. Texas A&M researchers define the Central Texas Triangle as an area encompassing the Dallas-Fort Worth Metroplex, Houston and San Antonio — using I-45 and I-35 as borders.

Two of the five fastest-growing cities in the U.S. (above 50,000 population) are suburbs of Austin. Consider the growth rates of Dallas’ southern suburbs along Interstate 35 between 2000 and 2010: Desoto, 30.28 percent; Glenn Heights, 54.71 percent; Red Oak, 93.10 percent; and Waxahachie, 38.36 percent. The explosion of Austin’s northern suburbs is well known, but for clarity their population increases look like this: Round Rock (38.80 percent), Georgetown (53.36) and Temple (20.22).

Do we still consider Dallas and Austin a 90-minute drive away? Perhaps, but reaching the edge of their respective urban sprawl is less than an hour’s drive from Waco. And let’s face it, in our culture distance equals driving time.

Waco is smack dab in the middle of a population-growth vise between the Metroplex and Austin. At this point, there’s really nothing that can stop our population from growing more rapidly than years (and decades) past. At some point, what’s happening in places like Waxahachie and Temple will happen here. The only question is how long will it take. Waco is a fairly isolated market along the I-35 corridor and one of the best-kept secrets in Texas. It also presents a different dynamic in the I-35 population boom. It is already a mid-sized city in little danger of “exploding” with growth. The kind of population explosion that happened in places like Frisco, McKinney and Rockwall transformed those hamlets into brand new cities.

According to official projections, there’s no need to start double-decking I-35 any time soon. The Office of the State Demographer predicts McLennan County will grow only modestly between 2010 and 2050 — showing at most a 50 percent population gain over 40 years, mirroring the long-held trend line of 1.25 percent growth per year.

Those projections defy logic, however. According to the Dallas Morning News, the Metroplex will add more than 1 million people in the next six years, and the Metroplex population will increase from 6.3 million to 16.7 million by 2050. Are we to believe that 10 million new residents will move in 90 miles up the interstate over the next 36 years and only a tenth of 1 percent will find their way here?

Austin added more to its population in real numbers than any other like-sized city in America last year. The population spike that hit Round Rock and Georgetown is already impacting Temple.

That’s a mere half-hour down the road.

Population experts say America’s migration south and west will continue and Texas will be the destination of choice over the next 20 years.

As the state’s big four metropolitan areas push outward, they’ll place once-isolated cities such as Waco into the big picture. And there’s no avoiding it.

Steve Boggs is editor of the Tribune-Herald. Email sboggs@wacotrib.com.