W. Donald Cousens (born July 20, 1938 in Vankleek Hill, Ontario) is a politician in Ontario, Canada. He was a Progressive Conservative member of the Legislative Assembly of Ontario from 1981 to 1994, and briefly served as a cabinet minister in the government of Frank Miller. Since 1994, he has served as the mayor of Markham.

Cousens was educated at Queen's University and Knox College at the University of Toronto. An officer in the Canadian Armed Forces, he served as an executive with Honeywell Ltd. before entering political life, and later became a chair of the York Technology Association . He was a member of the York County Board of Education from 1972 to 1979, eventually serving as chair. In 2003, he was award a Queen's Jubilee Medal .

Cousens was first elected to the Ontario legislature in the 1981 provincial election, defeating Liberal Alf Strong by fewer than 2,000 votes in the riding of York Centre. He served as a backbench supporter of Bill Davis's government for four years, and became parliamentary assistant to the Minister of Citizenship and Culture on February 25, 1985, when Miller replaced Davis as Premier of Ontario.

Although Cousens was re-elected with an increased plurality in the 1985 provincial election, the Progressive Conservatives were reduced to an unstable minority government. Cousens was appointed Minister of Correction Services on May 17, but accomplished little of consequence before the Miller government was defeated in the house on June 26. Along with other members of the Tory caucus, Cousens then moved to the opposition as Liberal David Peterson became Premier.

The Progressive Conservatives were reduced to only 16 seats in the 1987 provincial election. Cousens was able to defeat Liberal Gail Newall by under 1,000 votes in the new riding of Markham , although he held no official critic positions in the parliament which followed.

In the 1990 provincial elections, Cousens scored an impressive victory over Liberal Frank Scarpitti , winning by more than 10,000 votes. The Progressive Conservatives as a whole managed only a modest recovery, however, increased their caucus size from sixteen to twenty. Cousens served as his party's critic for Environment, Finance, and Citizenship, Race Relations and Human Rights at various times in next parliament. He also became a leading opponent of Liberal MPP John Sola in 1991, after Sola made comments about Canadian Serbs that were generally regarded as racist (Sola was later expelled from the Liberal Party).

On one occasion during his time as an MPP, Cousens brought forward a private member's bill to outlaw smoking in public places.

A Red Tory by inclination, Cousens played little role in the party's drift to the right under Mike Harris. He resigned his seat in the legislature on September 30, 1994 to run for mayor of Markham. He was the only member of the 1990 Ontario PC caucus not to seek re-election to the legislature in 1995.

Markham is a diverse community with a thriving economy, and has grown significantly under Cousens's watch. The city is debt free, and has gained many jobs in the software field. Unlike Mike Harris's provincial government, Cousens has been a supporter of photo radar to discourage speeding.

There is a Don Cousens Charitable Foundation within Markham.