Pierce and Snohomish counties are No. 1 and No. 2, respectively, nationwide for net population increase in 2015 and 2016 because of migration from other U.S. counties — out of more than 3,100 counties. That is the conclusion reached by the Seattle Times based on new U.S. Census Bureau data. Counties in California, Utah and Colorado were also in the top five.

Pierce County had nearly 12,000 more people moving in than out from within the U.S. last year, up from less than 5,000 in 2015. In Snohomish County, the jump in 2015 was 4,500 and 10,500 last year.

The Census Bureau does not collect the reasons for the moves, but one strong possibility is that at least some of the movers are coming from King County as rents and residential sale prices rise in the Seattle market. Even so, King County is still attracting people domestically, about 8,500 in the last two years. That is a switch from previous years, when King was the top draw in the region, more so than Pierce or Snohomish.

King County remains a strong attraction for international migration, which represented a net of 15,500 new residents from overseas during the last two years. That is at least six times more than either Pierce or Snohomish.