The incident started around noon Monday in the 6000 block of Lost Horse in the area of Citrus Avenue and Sierra Lakes Parkway.
Police say a woman was having an argument with a man - identified only as "Q" - and he then grabbed her 2-month-old baby girl and fled on foot.
Fontana police issued an alert asking the public to help them find Q and the baby.
Shortly after 8 p.m., the department announced the girl had been found safe. They did not specify if Q had been located or arrested, and what led to the child's recovery. They said an update would be provided Tuesday.
Anyone with information is asked to call Fontana police at (909)350-7700 or just dial 911.