The Werribee River is a perennial river of the Port Phillip catchment that is located on the expansive lowland plain southwest of Melbourne, Victoria, Australia. The headwaters of a tributary, the Lerderderg River, are north of Ballan near Daylesford and it flows across the basalt plain, through the suburb of Werribee to enter Port Phillip. A linear park follows the Werribee River along much of its course. In total the Werribee River completes a journey of approximately 110 kilometres (68 mi).

Victoria is a state in southeastern Australia. It is the second-smallest state, with a land area of 227,444 km2 (87,817 sq mi); the second-most-populated state, with a population of over 6.7 million; and the most densely populated state in Australia. Victoria is bordered by New South Wales to the north and South Australia to the west and is bounded by the Bass Strait to the south, the Great Australian Bight portion of the Southern Ocean to the southwest, and the Tasman Sea to the southeast. The state encompasses a range of climates and geographical features from its temperate coastal and central regions to the Victorian Alps in the northeast and the semi-arid northwest.