LYNN – Experts are mulling whether the state’s population decline could eventually result in the loss of a congressional seat.The concern was raised after U.S. Census Bureau statistics indicated an exodus from Massachusetts. Political observers questioned whether the decrease would impact the number of U.S. House of Representatives seats.The migration has been attributed to the high cost of living, particularly housing.U.S. Census data indicates the average cost of a single-family home in Massachusetts today is $185,700 while the national average is $119,600.Not everyone, however, was alarmed.”The Census population estimates are based on assumptions,” said U.S. Rep. John F. Tierney, a Salem Democrat who represents the 6th Congressional District, mostly on the North Shore. “We’ve actually seen reports that suggest the opposite is true in parts of Massachusetts.”According to Tierney, communities such as Georgetown, Groveland, Middleton, Danvers, Salem and Peabody have all experienced population growth in recent years.”Some rural areas are losing population. But before any changes are made, we would have to take a look at how things are going nationwide,” he said. “If there is a reduction at all, it might be that there are seats more vulnerable than those in Massachusetts, where our cities are growing. We’ve actually seen an influx of building permits and we know the 5th District is also increasing in population.”U.S. Census data updated through Jan. 12 shows Massachusetts’ population density at 809 people per square mile, compared to the national average of 79.6.Tierney noted that Secretary of State William Galvin recently called for a new initiative aimed at counting all those who live in Massachusetts, legally or otherwise.The state has an estimated 150,000 to 200,000 illegal immigrants who, for fear of arrest, do not respond to government census takers. If that were to change, and the illegal immigrants were counted as residents, no threat to a congressional seat would exit, according to Ali Noorani, executive director of the Massachusetts Immigrant and Refugee Advocacy Coalition.”This is for real,” Noorani said. “A congressional seat is on the line.”Massachusetts holds 10 of the 435 fixed seats in the House of Representatives, based on population. By contrast, Vermont has one. Each of the 50 states has two senators. Federal funding channeled to the states is also formulated on population. In most states, the number of seats also translates directly to political clout in the Electoral College. Massachusetts once had 30 House seats.”The Electoral College has always been disputed. The smaller states get more of an impact. I wouldn’t have a problem if it were no longer used. People could go to a straight vote,” said Tierney. “Take a vote of each state and tally that. In Maine, they attribute votes to a congressional district rather than statewide. In other states, it’s winner take all.”U.S. Rep. Edward Markey, a Malden Democrat, said the state has a major stake in ensuring that its population, estimated at more than 6.5 million, is counted accurately since millions of federal aid dollars are at risk.With Gov. Deval Patrick newly ensconced at the State House, Massachusetts could see its economic situation turn around, and any migration of young residents to the South and West stanched, Tierney said.The next U.S. Census isn’t due until 2010, but Boston-based Census officials say steps are already being taken to assure an accurate count.