Minnesota is teetering on the border line between losing one of its eight U.S. House seats and keeping them all, if projections for the 2010 census prove accurate. The outcome could hinge on counting or overlooking as few as 1,800 Minnesotans, state demographer Tom Gillaspy said Monday.

The distribution of the 435 House seats among the states is determined after each 10-year census, when districts are reapportioned in response to population shifts.

Every state is guaranteed at least one House member, and the remaining 385 seats are distributed according to a formula based on population size. It is a calculation that has not changed since the early 1940s.

That's where the math gets tricky.

As a state's population decreases or grows more slowly than other states', it rises on the list of potential seat losers. Lost seats offset the seats gained by faster-growing states. Total House membership must remain at 435 members, where it has been since 1910. House districts must be as equal in size as possible, but each district must be contained within a single state.

Fast-growing Sun Belt states such as Texas are expected to pick up as many as four seats after the next census. Arizona is projected to pick up two, and Florida, Georgia and North and South Carolina are expected to gain one each.

Northern and Rust Belt states are projected to lose seats.

New York and Ohio, for instance, could lose two seats each, while Pennsylvania, Michigan, Illinois, Iowa and Minnesota are projected to each lose one apiece.

Seats in Congress are not only a matter of pride for a state but can also affect its success in advancing its interests in Washington.

A close call

Gillaspy, the state's chief contact for the federal census, said the most recent projections for Minnesota show the state falling 1,800 people short of being able to keep its eight seats. To put that in perspective, Minnesota's population "grows" by about 900 people a week, meaning people move in and babies are born that much faster than people move away or die.

"Minnesota is just under the cut-off point for the last congressional seat, but it's all very, very close," Gillaspy said. "It's almost like the Senate race. It's about as close as you can get."

If the number falls below the threshold after the 2010 census, the Legislature will begin a redistricting process to divide the state into seven more or less equal districts rather than eight.

The end result could be two incumbents facing off against each other, and the political landscape of the state could change dramatically, opening partisan wounds.

It's possible that portions of the fast-growing Sixth District, which includes St. Cloud and the northern Twin Cities suburbs, could be included in the slow growth Seventh or Eighth districts of northern Minnesota. Or portions of the burgeoning Second District, which includes the southern Twin Cities suburbs, could be absorbed into congressional districts near St. Paul or Minneapolis, where population growth has also slowed. Another long-debated possibility would combine the two urban districts.

"That's the kind of partisan decisionmaking I don't get involved in," Gillaspy said. "When I get the data, I'm just going to throw it in the cage and run."

But Minnesota, which lost a ninth House seat in 1960, could avoid another loss with a strong census count in 2010, especially with the cut-off number so close.

Gillaspy and other officials will be making that point today when a federal census office opens in St. Paul, and they will begin a campaign to remind people how important it is to participate.

"If we can make sure we count everybody here, that could be as much as half a percent or quarter percent difference, and that could be enough," he said.

Mark Brunswick • 651-222-1636