1885-1918: The Sessional Divisions of Brentwood (except the civil parishes of Rainham and Wennington) and Chelmsford.
1918-1950: The Municipal Borough of Chelmsford, the Urban District of Brentwood, the Rural Districts of Chelmsford and Ongar, and in the Rural District of Billericay the civil parishes of Hutton, Ingrave, Mountnessing, Shenfield, and South Weald.
1950-1955: The Municipal Borough of Chelmsford, and the Rural Districts of Chelmsford and Ongar.
1955-1974: The Municipal Borough of Chelmsford, and the Rural District of Chelmsford.
1974-1983: The Municipal Borough of Chelmsford, and in the Rural District of Chelmsford the civil parishes of Danbury, East Hanningfield, Great Baddow, Highwood, Ingatestone and Fryerning, Little Baddow, Margaretting, Mountnessing, Rettendon, Runwell, Sandon, South Hanningfield, Stock, West Hanningfield, and Woodham Ferrers.
1983-1997: The Borough of Chelmsford wards of All Saints, Baddow Road, Boreham and Springfield, Cathedral, Danbury and Sandon, East and West Hanningfield, Galleywood, Goat Hall, Great Baddow Village, Highwood and Margaretting, Little Baddow, Mildmays, Moulsham Lodge, Oaklands, Patching Hall, Rothmans, St Andrew's, Stock, The Lawns, and Waterhouse Farm.
2010-present: The Borough of Chelmsford wards of Chelmer Village and Beaulieu Park, Galleywood, Goat Hall, Great Baddow East, Great Baddow West, Marconi, Moulsham and Central, Moulsham Lodge, Patching Hall, St Andrew's, Springfield North, The Lawns, Trinity, and Waterhouse Farm.
Following the Boundary Commission review of parliamentary representation in 2008 Parliament created a new Chelmsford constituency which had for the previous three elections been split in two halves and included more surrounding rural settlements. A majority of the electorate for this new constituency comes from the previous West Chelmsford constituency. A smaller element (Great Baddow and outskirts) comes from the Maldon & East Chelmsford constituency.
The constituency is contained entirely within the Borough of Chelmsford which is larger and also contributes to the Maldon and Saffron Walden constituencies.
At its first contest in 2010, the seat was closely fought by the Conservatives and the Liberal Democrats, who finished less than 10% apart, with Conservative candidate Simon Burns (the former MP for West Chelmsford) being elected. Labour polled 11%, despite having been only around 100 votes behind the Liberal Democrats in West Chelmsford in 2005, and even taking second place in 2001.
Chelmsford had its own constituency from 1885 until its abolition in 1997. During its latter years, the old seat was narrowly won by a Conservative over a strong Liberal Democrat performances, including their predecessor party the Liberal Party. The constituency was recreated in time for the 2010 general election.
* Served in the 2005–2010 Parliament as MP for West Chelmsford
General Election 1939/40:
Another General Election was required to take place before the end of 1940. The political parties had been making preparations for an election to take place from 1939 and by the end of this year, the following candidates had been selected;Conservative: John Macnamara
Labour: Dr Mary Day
endorsed by Coalition Government