The investigators searched the 7th-arrondissement house of the former prime minister, who faces calls to drop out over allegations he gave fake jobs to family members. Fillon was in the southern city of Nimes for a campaign function. His parliamentary office was similarly searched last month.
Last week, a formal judicial investigation was opened in response to allegations against Fillon of "misuse of public money". The conservative politician will appear before magistrates on March 15.
Fillon had earlier said he would quit the race if a formal investigation was opened. He is denying any wrongdoing and has said he will cooperate with the judiciary. The allegations, dating back to January, were made by the investigative weekly Le Canard Enchaine.
The weekly claimed, citing pay slips, that Fillon had paid about €1 million ($1.08 million) out of public funds to his wife and two children as parliamentary assistant and legal consultants, respectively.
Although it is legal for French lawmakers to hire family members as parliamentary assistants, Le Canard Enchaine cast doubts over whether his wife Penelope actually performed aide duties. A primary investigation was launched after the first report came out on Jan. 25. It was later widened to include two of the Fillons' five children, Marie and Charles.