There are no formal or legal definitions of this district but a loose definition would be that it stretches from the M2 Hills Motorway in the south to the Hawkesbury River in the north and Old Windsor Road in the west to Pennant Hills Road and Berowra Creek in the east.

The Dharug People occupied the Hills and surrounding areas prior to European settlement.

In the same year, William Joyce, a pardoned convict, received the first land grant in the area, east of Hawkesbury Road, in what is now Baulkham Hills.

In 1799, Joseph Foveaux was granted 300 acres of land in what is now the Bella Vista area of Baulkham Hills.

Over 200 convicts escaped from a prison farm with the intent to "capture ships to sail to Ireland".

They connect Parramatta with Windsor, but are majorly used as arterial roads for residents, especially in the Hills District.

New Windsor Road was completed in 1812, featuring 70 bridges, and was 32 feet wide (approximately 10 metres).

As the name indicates, the Hills District is an area of high elevation above sea level (compared with the rest of the Sydney basin) and thus creates orographic rainfall brought in by onshore winds from the Pacific Ocean.

This climate characteristic was well suited to orchard production of stone fruit and citrus which proved luxuriant on the deep rich soils.

The area was previously known to have the highest rate of religious service attendance in Australia and was referred to as "Sydney's Bible Belt".

[7] Despite a high Christian population, the area no longer represents the most religious region of Sydney.

The federal Division of Mitchell, which covers most of the area, is one of the safest seats in metropolitan Australia for the conservative Liberal Party of Australia, and all of the Hills District seats in the New South Wales Legislative Assembly are held by the NSW Liberals.

The Metro North West Line, opened in May 2019, has a frequency of every 4 minutes in the peak hour to Chatswood railway station, where passengers can change to other trains towards the city.

The local community radio station for the district is Alive 90.5 which is based in Baulkham Hills and also broadcasts to Parramatta and Cumberland.