The average residential assessment in Suffolk decreased by 4 percent, City Assessor Sid Daughtrey said Wednesday.

Daughtrey told the City Council at their meeting Wednesday that assessing properties had been a difficult process this year because of the high number of foreclosures and the low number of real estate transactions that occurred in 2009. Overall assessments, including commercial, residential and agricultural uses, decreased by an average of 2.5 percent.

The year 2009 had only 1,926 real estate transactions, compared with 4,060 in 2005. Foreclosures, on the other hand, increased sevenfold, going from 45 in 2005 to 315 in 2009.

Assessment notices will be mailed to owners Friday, Daughtrey said.

Assessments varied widely throughout the city, decreasing by 17 percent in Hillpoint Commons and increasing by 10 percent in the Boston and Williamstown area. Daughtrey said that moderately-priced homes were more likely to see an increase in their assessment because there is more of a market for them than for high-priced homes.

Owners who do not like their reassessment have a grievance process. First, owners should call 514-7475 to schedule an informal meeting with the assessor who dealt with their property. If the meeting does not resolve the owner’s concerns, he can file an application with the Board of Equalization, which is made up of property owners in Suffolk appointed by the Circuit Court. Those not satisfied with the board’s decision can appeal to the Circuit Court.

Several programs exist to help qualifying property owners with their tax bill. People over age 65 or who are totally disabled can have a portion of their tax bill forgiven if the owners have a combined gross income of less than $54,242 and a net worth, exclusive of the home and 10 acres surrounding it, less than $243,101. For more information, contact the Department of Social Services at 514-7450.

For land that is used as agricultural, horticultural, forest or open space, owners also can receive an abatement on their tax bill. The Agricultural Abatement Program bases the assessment on use value rather than market value. For more information, call 514-7475.

For properties that have been rehabilitated, the value of qualifying improvements to residential or commercial buildings more than 25 years old can be forgiven for 10 years. For more information, call 514-7475.