The figure was presented by Exchequer Secretary David Gauke in response to a written question submitted in Parliament by Conservative MP Dr Sarah Wollaston.
Of the 685 staff, 153 are involved in detection work, 360 are assigned to investigation duties and 172 are focused on intelligence gathering.
Their combined salaries come to £34.1 million, averaging at just under £50,000 per employee.
HMRC spent £170,000 on targeted media campaigns to tackle tobacco smuggling in 2009-10, Gauke added.
The department calculates that illicit tobacco costs the UK around £10 million a day in lost tax revenue. Last month HMRC said: “HMRC is cracking down on tax fraud, including duty evasion from illegal, smuggled tobacco.
“The government has made a further £900 million available to us to tackle evasion, avoidance and attacks by criminal gangs. We will use this money to increase tax revenues by £7 billion a year by 2014-15.”