Almost half of the state's jurisdictions lost more people than they gained in 2007, the data shows.
The state's two biggest counties -- Montgomery and Prince George's -- as well as Baltimore City lost thousands of people.
In total, about 36,000 more people left Maryland last year than moved to the state, according to the data.
"Overall, there is a net movement of people out of the state, which is in sharp contrast to what is happening in Washington County," Bernstein said.
For the last three years, Washington County has gained more people than it has lost and has led the state in internal migration, which is one of three components of Census population estimates.
The other two components of population change are natural increase (the number of births minus deaths) and international migration, or how many people moved between the county and foreign countries.
Births have risen steadily in Washington County over the last several years while deaths have remained relatively constant, according to the data.
There were 1,946 births in the county in 2007, compared to 1,874 in 2006 and 1,710 in 2005, the estimates show.
Over that same period, the number of deaths hovered around 1,270.
International migration has been minimal in Washington County.
The county's population topped 145,000 in 2007, according to the Census estimates.
It rose to 145,113 in 2007 from 143,334 in 2006.
The Census bases its data on Medicare enrollment records, tax returns, birth and death records, and other Census studies, Bernstein said.