Forbes has created an interactive map visualizing migration data into and out of US counties. It’s based on IRS data from 2008-2009 so only taxpayers and dependents are included. The black lines represent people moving to a certain place, the red lines are people moving out.
I used to live in Portland and it seems it’s getting really crowded there. You can get detailed information at the web site. 141 people moved from Hennepin County to Multnomah County and 90 people moved from Multnomah County to Hennepin County.
For curiosity I also checked out Beltrami County (where Bemidji is located). Not much change. Except for 23 people who moved to Arizona (seems like a data error), nobody moved further away than the cities and hardly anyone moved there.