A federal judge in Houston also ordered Kline Fisher Budd of the Conroe area to repay more than $243,000. Budd in August pleaded guilty to theft of government property.
Officials in late 2010 began to review benefits for Willa Mae Shaughnesy, who at the time would have been 104 years old.
Authorities located a death certificate that indicated Shaughnesy died in November 1984. Prosecutors say the woman and her son had a joint bank account and her Social Security benefits kept being electronically deposited.
A judge accepted the plea agreement Friday and took into consideration Budd's age and health issues when sentencing him to prison.