Paul Vikner, Mack Trucks' president, introduced Snow - who is fifth in the presidential line of succession - as "our most distinguished guest ever."
"Because of investment outside the U.S., there are more jobs inside the U.S.," Snow told the crowd. "They raise the living standards of Americans."
Sten-ke Aronsson, the senior vice president of Volvo Powertrain North America, told The Herald-Mail that Snow's office called Volvo last week to request the tour, which Aronsson led.
Treasury Department spokeswoman Brookly McLaughlin said Snow makes business visits like Thursday's "on a fairly regular basis." She also did not directly answer whether the tour was a reaction to the ports deal.
Volvo Powertrain North America - a division of the Volvo Group, which is based in Sweden - is in the midst of a $150 million upgrade of the Washington County plant.
The plant produces heavy-duty and medium-duty truck engines and transmissions for Volvo and Mack.
At the back of the tour group, Washington County Commissioners President Gregory I. Snook repeatedly stopped to chat with employees he knew.
Snook later said he was an assembly supervisor at the plant for about two years in the mid-1980s and has relatives who work there now.
In 2002, one year after acquiring Mack and Renault, Volvo announced it would build all of its North American truck engines in Washington County. At the time, the Hagerstown-Washington County Economic Development Commission said Volvo had considered sites in Pennsylvania, South Carolina and Mexico.
The $150 million upgrade launched in 2004 was another positive sign.
"When this investment came in, to me, it means that they're staying," Snook said.
With about 1,200 employees, Volvo Powertrain North America is the sixth-largest employer in the county and the largest foreign-based company.
Timothy Troxell, the executive director of the Hagerstown-Washington Economic Development Commission, who also was on the tour, named other examples.
They included: Saputo Cheese USA, which is in Hancock and based in Canada; Maccaferri Gabions, which is near Williamsport and based in Italy; and Rampf Molds Industries, which is in Hagerstown and based in Germany.
The EDC's annual Business & Industry Directory says companies based in Australia, Japan, the Netherlands and Switzerland also operate in Washington County.