Ridge said in his letter that the assault by Matthew Lazenby, 21, was out of character and that Lazenby was sincerely remorseful.
"As reprehensible as his actions were that bring him before you, they were clearly not a reflection of a general pattern of violent or abusive behavior," Ridge said in the letter, which did not ask the judge for a specific sentence.
The Erie (Pa.) Times-News said Wednesday that Ridge's letter did not appear to help Lazenby a great deal since he was sentenced to four to eight years in prison for aggravated assault.
Lazenby pleaded guilty to striking and shaking his then-girlfriend's 2-year-old daughter, Autilli Teribery, last Halloween at the woman's home in Erie. The child suffered a fractured skull and potentially long-term neurological injuries.
The Times-News said Lazenby, who had been drinking, became angry after the little girl's mother left her alone with him.
Ridge, who was also the first U.S. Secretary of Homeland Security, has been Lazenby's neighbor in Millcreek Township for 10 years.