[3] Ulrich von Cossonay gave the village church to the monastery in Romainmôtier in 1096.

In 1224, it passed to the Benedictine monastery in Lutry, which built a priory in the second half of the 13th century.

The Barons of Cossonay ruled over a territory from La Chaux to Boussens and from Dizy to Gollion.

When the canton of Vaud was conquered by the Bernese in 1536, the town came under the administration at Morges.

The district of Cossonay was formed in 1798, and the municipality was its capital from its inception to its dissolution.

Cossonay lies at an elevation of 562 m (1,844 ft) and 14 km (8.7 mi) northwest of Lausanne.

In the south, it reaches down to the valley of the Valezard, and in the north to Pré Defour.

Cossonay has an area, as of 2009[update], of 8.29 square kilometers (3.20 sq mi).

[5] The municipality is located on a plateau, that rises steeply about 130 m (430 ft) above the Venoge river.

The area of Grands Moulins, the cable works of Cossonay, the train station and the settlement of Cossonay-Gare are at the foot a hill that lies in the municipality of Penthalaz.

The surrounding municipalities are Penthalaz, Gollion, Senarclens, La Chaux, Dizy, and Lussery-Villars, all in the same district.

The blazon of the municipal coat of arms is Per pale Azure and Argent.

[8] The age distribution, as of 2009[update], in Cossonay is; 402 children or 12.1% of the population are between 0 and 9 years old and 488 teenagers or 14.7% are between 10 and 19.

The entire town of Cossonay and the village of La Chaux is part of the Inventory of Swiss Heritage Sites.

[9] There were 1,388 residents of the municipality who were employed in some capacity, of which females made up 44.1% of the workforce.

In the tertiary sector; 162 or 21.4% were in wholesale or retail sales or the repair of motor vehicles, 30 or 4.0% were in the movement and storage of goods, 57 or 7.5% were in a hotel or restaurant, 5 or 0.7% were in the information industry, 166 or 22.0% were the insurance or financial industry, 30 or 4.0% were technical professionals or scientists, 102 or 13.5% were in education and 92 or 12.2% were in health care.

[9] From the 2000 census[update], 763 or 29.8% were Roman Catholic, while 1,183 or 46.2% belonged to the Swiss Reformed Church.

The wettest month is June during which time Cossonay receives an average of 93 mm (3.7 in) of rain or snow.

The driest month of the year is April with an average of 64 mm (2.5 in) of precipitation over 9.4 days.

In the Vaud cantonal school system, two years of non-obligatory pre-school are provided by the political districts.

The canton's primary school program requires students to attend for four years.

[17] Cossonay lies at the crossroads of the highways from Morges to Orbe and from Lausanne over Col du Mollendruz to the Vallée_de_Joux.

[21] Postal buses run from Cossonay-Gare to Cheseaux-sur-Lausanne and L'Isle, as well as from Cossonay-Ville to Cottens and to Morges.