The assaults took place in Beccles, Suffolk, and in the Hales and Thetford areas of Norfolk between 1999 and 2003.
Rodney Scott, 72, of Firfield Close, Beccles, had already pleaded guilty to eight counts of indecent assault at Ipswich Crown Court.
He was given a prison sentence of six years and eight months.
Det Con Kate Bond said: "The victim has to be commended for her courage in coming forward and reporting the incidents to us, and she wanted to say that she has been overwhelmed by the support offered to her by the team and the belief that they have shown in her.
"The result at court today has exceeded her expectations."
A pensioner has been jailed for repeatedly sexually assaulting a girl under 16.