The first phase, Erin Mills South, known later as Erin Mills, was built beginning in the early 1970s continuing through the decade. A display centre formerly built to serve home buyers and residents as a meeting hall, etc. was closed in the early 1980s and was transformed into the large, popular nightclub "Richard's". This club was closed in the early 1990s due to noise concerns from nearby residents and the building sat empty for many years until being torn down later that decade.
Erin Mills West, phase 2 of the "New Town" development, was completed in the mid-1980s. This area was part of the town of Oakville until 1974 when with the advent of regional government, the city of Mississauga was established and its westerly boundary was extended to 9th line north of Dundas Street West. These lands then became part of Mississauga.
Erin Mills Central, phase 3, is for the most part fully developed. This section contains everything from hi-rise condominiums to large low density housing. Its focal point is the Erin Mills Town Centre, which was completed in 1989. Credit Valley Hospital, the largest in Mississauga, is located in this area. The older village of Streetsville sits adjacent to Erin Mills Central to the east, running along the Credit River. Both areas are connected closely, even in the context of Mississauga as a whole. For example, the Streetsville GO station serves as a commuter point for many Erin Mills residents travelling to work in Toronto and Streetsville residents use Erin Mills Town Centre as their primary retail shopping centre. The telephone exchanges in Erin Mills are referred to as "Streetsville exchanges", even though most are not located in the older section of the village.
Churchill Meadows, phase 4, was mostly developed from 2000 to 2010. The largest as yet undeveloped parcels in this phase are the 20 hectare McCracken Farm on Tenth Line, to be developed for semi-detached houses, and a 43 hectare property on Eglinton Avenue, to be developed for employment uses and a high school. Much of the new subdivisions are low to medium density residential, and as with the previous phases, land for parks has been protected from development. Unlike the previous phases, Churchill Meadows was built with a relatively permeable street network, and creek courses were not preserved. This section of Erin Mills borders the mostly rural section of the town of Milton, located to the west. The older suburban development of Meadowvale borders the area to the north.
All four sections described above are generally not referred to by locals as "west", "central", etc. but rather Erin Mills on the whole, the geographic distinctions were used by land developers to indicate the phasing of development.
To the south of Erin Mills (south of Dundas Street, north of the QEW), lies the older housing area of Sheridan Homelands and adjacent employment lands of Sheridan Park. This area is sometimes lumped in with Erin Mills by both locals and others when referring to a location within it.
The lack of a sustainable high use transit corridor has prevented Erin Mills from achieving higher densities, although there are some hi-rise condominium and rental units, some currently under construction. The area has an inter-connected and heavily forested recreational trail system.