The change, however, might not reduce their tax bills by very much.
The state Department of Assessments and Taxation, citing this year's calculations, said residential property values have dropped an average of 3.4 percent since those homes were last assessed in 2005.
The drop comes after years of significant increases and is a sign that home prices have dipped in a stagnant market.
In some areas of the state, residential and commercial assessments conducted this year rose over those done three years ago. Prince George's County is one of those.
But the increases were a long way from the double-digit hikes of recent years. Assessments done this year were 4.9 percent higher than three years ago; assessments done last year were 51.6 percent higher than in 2004.
The drop would likely be steeper if assessments were compared with those from last year. Maryland's assessing of properties every three years helps minimize the upswings and downturns of the real estate market.
Montgomery County saw one of the state's most dramatic drops; residential and commercial property values fell an average of 3.5 percent from three years ago. Home values dropped an average of 16.3 percent in Montgomery. There, about 118,000 homes were re-evaluated this year -- in Montgomery Village, parts of Rockville, parts of Silver Spring, Sandy Spring and Olney.
Some 80,000 homes were assessed this year in Prince George's, mostly in Suitland, District Heights, Landover and Capitol Heights.
James Soresi is supervisor of assessments for the county. He said values held up better in Prince George's than in other parts of the state partly because the communities examined were some of the county's most affordable areas, where homes continue to sell at a good pace.
"We still have a lot of sales activity," he said.
Many residents won't see much of a change in their annual tax bills, regardless of the reassessment, because of the state's Homestead Tax Credit. The credit is designed to ease the effect of rapidly rising assessments in hot real estate markets, setting a limit for the amount any homeowner's assessment can rise in a given year.
In years when assessments go up by less than the cap, however, increases from past years, deferred by the credit, are phased in. Therefore, many longtime homeowners have their assessments rise by about the same amount each year, regardless of new valuations.
In Montgomery, assessments cannot increase more than 10 percent in a year. In Prince George's, the limit is 5 percent, and in Anne Arundel County, where values dropped by an average 0.1 percent from three years ago, the limit is 2 percent.
"Don't be surprised," said David Platt, chief economist for the Montgomery Department of Finance. "Just because this assessment goes down doesn't mean your taxable assessment goes down."
In Howard County, assessments fell an average 0.8 percent. Average values fell by 1.5 percent in Charles but went up by 1 percent in Calvert County and 2.7 percent in St. Mary's.
Soresi urged taxpayers to examine their assessment notice carefully to make sure that tax officials have properly noted whether a residential property is a primary residence. Only owner-occupied primary homes qualify for the tax credit, he pointed out.
Taxpayers have 45 days to appeal assessments.