Sir Graham Robert Watson (born 23 March 1956) is a British Liberal Democrat politician.
 He served as a Member of the European Parliament for South West England from 1994 until 2014 and was the leader of the Group of the European Liberal Democrat and Reform Party 2002–2004 and the first leader of the Group of the Alliance of Liberals and Democrats for Europe 2004–2009.
 From 2011 until 2015 he was the President of the ALDE Party.
The Group of the European Liberal Democrat and Reform Party (French: "Groupe du parti européen des libéraux, démocrates et réformateurs" , ELDR) was a liberal political group in the European Parliament between 1976 and 2004.
 The group comprised the European Liberal Democrat and Reform Party and its constituent national-level parties, variously of liberal, centrist and agrarian orientation.
Jennifer Nancy Willott (born 29 May 1974) is a British politician.
 She was the Liberal Democrat Member of Parliament for Cardiff Central from 2005 to 2015.
 Willott became a junior minister in the Department for Business, Innovation and Skills and Government Equalities Office in December 2013, temporarily standing in for Jo Swinson while she was on maternity leave.
 She is the first woman and first Liberal Democrat to represent her seat.
 She was a councillor in the London Borough of Merton from 1998 to 2000.
George Lyon (born 16 July 1956) is a Scottish Liberal Democrat politician, and a former Member of the European Parliament for Scotland.
 Lyon is a former farmer from the Isle of Bute, and previous National Farmers Union of Scotland president.
 From 1999 to 2007 he was the Member of the Scottish Parliament for Argyll and Bute, and served as both Chief Whip and Deputy Finance Minister.
 A member of the Alliance of Liberal Democrats in Europe (ALDE) group whilst in the European Parliament, Lyon was lead spokesperson for ALDE on the Agriculture Committee.
 Lyon was also vice-chair of the EP's Budget Committee.
Fiona Jane Hall MBE (born 15 July 1955 in Swinton, Lancashire), née Cutts, was a Member of the European Parliament for North East England and leader of the Liberal Democrat MEPs., until the 2014 European Election.
 She was elected to the European Parliament in 2004, and re-elected in 2009, coming in third behind Labour and Conservative candidates with 17% of the vote, the highest of any UK Liberal Democrat candidate.
Meral Hussein Ece, Baroness Hussein-Ece, (born 10 October 1953) is a British Liberal Democrat member of the House of Lords.
 She is the first woman of Turkish Cypriot origin to be a member of either house of Parliament after she was appointed a Liberal Democrat working peer on 28 May 2010.
 She has been the Liberal Democrat Spokesperson for Equalities since 2015.
James Thorne Erskine, 14th Earl of Mar and 16th Earl of Kellie, {'1': ", '2': ", '3': ", '4': "} (born 10 March 1949) is a British peer and former Liberal Democrat member of the House of Lords.
Diana Paulette Wallis, {'1': ", '2': ", '3': ", '4': "} (born 28 June 1954 in Hitchin, Hertfordshire) is a British former Liberal Democrat Member of the European Parliament (MEP) for Yorkshire and the Humber.
 Wallis was first elected in 1999 and re-elected in 2004 and in 2009.
 She resigned her seat in January 2012.
 On 26 April 2013, she became an Honorary Fellow at the Law School of the University of Hull (UK).
Hertfordshire ( ; often abbreviated Herts) is a county in southern England, bordered by Bedfordshire to the north, Cambridgeshire to the north-east, Essex to the east, Buckinghamshire to the west and Greater London to the south.
 For government statistical purposes, it is placed in the East of England region.
Michael Douglas Thornton (born 1 May 1952) is a British politician and former Liberal Democrat Member of Parliament for Eastleigh in Hampshire.
 He was elected in the Eastleigh by-election held on 28 February 2013, a seat which he lost at the 2015 general election.

Question: Which county in England is home to British former Liberal Democrat Member of the European Parliament, Diana Wallis?
Answer: Hertfordshire