Here we go again.The 2020 U.S. Census, a decennial headcount of every person living in the United States, is still a year away. But local, state and federal officials in January officially kicked off the process in Massachusetts.“When people think of the 2020 census they think about just counting numbers, but we’ve been working on this now for three years,” said John Barr, census program manager at the Massachusetts Secretary of the Commonwealth.