Baulkham Hills (/bɔːlkʌm/;) is a suburb in the Hills District of Greater Sydney, in the state of New South Wales, Australia. It is located within 30 kilometres (19 mi) north-west of the Sydney central business district mostly within the local government area of The Hills Shire, of which Baulkham Hills was formerly the administrative seat and namesake of The Hills Shire. A small section of the suburb which is located south of the Hills Motorway-Windsor Road intersection is part of the City of Parramatta.

Baulkham Hills is predominately a residential suburb of the Hills District. Baulkham Hills Junction is the intersection of three major roads; Windsor Road, Old Northern Road, and Seven Hills Road. The suburb is bounded by Old Windsor Road and the North-West T-way in the west; Junction Road in the south which is parallel to the Hills Motorway, forming part of the National Highway.

The land that is now called Baulkham Hills was originally home to the Bidjigal people, who are believed to be a clan of the Darug people, who occupied all the land to the immediate west of Sydney. The best-known Aboriginal person from that time is Pemulwuy, a Bidjigal leader who led the Indigenous resistance movement against the British forces, including sacking farms in Castle Hill, before his eventual capture and execution by the British militia.

The Bidjigal people are today commemorated by Bidjigal Reserve which straddles the suburbs of Castle Hill, Baulkham Hills, North Rocks, and West Pennant Hills.

The first European settler in the Baulkham Hills Shire was William Joyce, who arrived in Australia in October 1791. In December 1794, he was given a grant of 30 acres (121,000 m²) in what became Baulkham Hills. He built a farmhouse on this land, but it was damaged by a fire in 1804, so he rebuilt it. The house still stands; however, it is now on a 2,055 m² property which backs onto Old Windsor Road. The suburb was largely made up of land grants until the mid 19th century, when many of these started to be subdivided into farms. This was accelerated by the construction of the Rogans Hill Railway Line. Urban developments were expedited from the 1960s. The name Baulkham Hills was given to the area by Andrew McDougall, a settler from Buckholm Hills, County of Roxburgh, Scotland. The name, which reminded McDougall of his homeland, was officially recognised in 1802. Baulkham Hills Post Office opened on 1 April 1856.

On 29 June 2018, northern portions of the suburb of Baulkham Hills were proclaimed as parts of the new suburbs of Norwest and Bella Vista. This area contained the commercial district of Norwest Business Park, which is no longer within Baulkham Hills.

Baulkham Hills has a number of heritage-listed sites, including:

According to the 2021 census, there were 37,415 residents in Baulkham Hills. 56.8% of residents were born in Australia. The most common countries of birth were China 8.2%, India 7.5%, England 2.3%, South Korea 2.1% and Sri Lanka 1.7%. 55.6% of residents spoke only English at home. Other languages spoken at home included Mandarin 10.2%, Cantonese 4.2%, Hindi 3.2%, Korean 2.8% and Tamil 2.1%. The most common responses for religious affiliation were No Religion, so described 29.7%, Catholic 23.4%, Anglican 10.8% and Hinduism 8.9%. The median weekly house hold income was $2474