Population growth in St. Croix County in western Wisconsin will more than double in the next 26 years, new demographic projections show.

Migration from the Twin Cities will swell the number of residents by 2035 to about 148,000 -- from 63,155 in the 2000 census -- with towns and villages such as Somerset, Hammond, Baldwin and Roberts more than doubling in size. Other big gains will come in the cities of Hudson, New Richmond and River Falls.

"The pattern there is largely suburbanization of the Twin Cities metro area," said David Egan-Robertson, the Wisconsin Department of Administration research analyst who compiled the report.

The projected growth is part of a continuing wave of expansion into exurban counties, including Wright, Sherburne, Isanti and Chisago, said Tom Gillaspy, Minnesota's state demographer.

"We've been growing outward in all directions and little things like state boundaries don't stop people," he said. "Americans have a real desire to find elbow room. That's a long-standing tradition."

In St. Croix County, a commuter mecca for residents who work in Minneapolis and St. Paul, the projected gain of 84,888 residents by 2035 ensures the county's status as the fastest-growing of Wisconsin's 72 counties, according to the report.

People move to the county for different reasons, demographers say, which could include their individual perceptions of zoning regulations, land values and tax rates. But the march to St. Croix County -- the latest numbers show an even greater influx of people than expected earlier -- concerns some Stillwater leaders who say commuter traffic leading to the city's 1931 lift bridge already clogs city streets.

One advocate for a new bridge across the St. Croix River is Gary Kriesel, who represents Stillwater on the Washington County Commission.

"Not building the bridge isn't going to stop that growth," he said.

Bill Rubin, executive director of the St. Croix Economic Development Corp., said his county suffers from the same economic downslide that's hitting everywhere. Plastics manufacturers in the county that make products for medical companies continue strong, he said, but throughout the county housing starts fell in recent years while foreclosures climbed.

"They've taken into consideration a lot more growth than I envisioned," said Rubin, who agrees that St. Croix County is more and more resembling the metro area. "To me, it's just very reflective of the Twin Cities and this notion that the I-94 corridor rolls right through the county."

Even with the decline in construction, population growth is evident in the volume of 911 calls, arrests and contacts with the county's human services department, said Chuck Whiting, the county's administrative coordinator.

"Right now, it's kind of hard to look out too far," he said. "You have to assume there'd just be more people everywhere and we'll get our share."

Egan-Robertson said the projections don't take the current economic downslide into account, in big part because demographers can't predict when the economy might improve. Numbers for 2035 were structured on historic data of births, deaths and migration patterns, he said.

Gillaspy said he expects to see some slowing in growth projections as residents adapt to higher energy prices. In addition, he said, a graying of the metro area means more residents will prefer to stay closer to services in Minneapolis and St. Paul than move farther into the country.

"Buying that big old prairie home isn't that big of a deal like it was 10 years ago," he said.

Kevin Giles • 651-298-1554