Western Mass. Senate Districts, west to east, source: http://www.mass.gov/

Benjamin Downing is the incumbent Senator in the Berkshire, Hampshire and Franklin District, consisting of Adams, Alford, Becket, Cheshire, Clarksburg, Dalton, Egremont, Florida, Great Barrington, Hancock, Hinsdale, Lanesborough, Lee, Lenox, Monterey, Mount Washington, New Ashford, New Marlborough, North Adams, Otis, Peru, Pittsfield, Richmond, Sandisfield, Savoy, Sheffield, Stockbridge, Tyringham, Washington, West Stockbridge, Williamstown and Windsor, in the county of Berkshire; Chesterfield, Cummington, Goshen, Huntington, Middlefield, Plainfield, Westhampton, Williamsburg and Worthington, in the county of Hampshire; and Ashfield, Charlemont, Conway, Hawley, Heath, Monroe and Rowe, in the county of Franklin.

Stanley Rosenberg is the incumbent Senator in the Hampshire and Franklin District, consisting of Northampton, Amherst, Belchertown, precincts A and D, Hadley, Hatfield, Pelham and South Hadley, in the county of Hampshire; and Bernardston, Buckland, Colrain, Deerfield, Erving, Gill, Greenfield, Leverett, Leyden, Montague, New Salem, Northfield, Shelburne, Shutesbury, Sunderland, Wendell and Whately, in the county of Franklin.

James T. Welch is the incumbent Senator n the Hampden District, consisting of Chicopee, ward 2, precincts A to D, inclusive, ward 4, precincts A to C, inclusive, ward 5, precincts A and B, and Springfield, wards 1, 3 and 4, ward 5, precincts A and B, ward 6, and Agawam and West Springfield.

Gale Candaras is the incumbent Senator in the First Hampden and Hampshire District, consisting of Springfield, ward 2, ward 5, precincts C to H, inclusive, wards 7 and 8, East Longmeadow, Hampden, Longmeadow, Ludlow and Wilbraham, in the county of Hampden; and Belchertown, precincts B and C, and Granby, in the county of Hampshire

Michael R. Knapik is the incumbent Senator in the Second Hampden and Hampshire District, consisting of Chicopee, ward 1, precincts A and B, ward, 3, precincts A to C, inclusive, ward 6, precincts A and B, ward 7, precincts A and B, ward 8, precincts A and B, ward 9, precincts A and B, Holyoke, Westfield, Blandford, Chester, Granville, Montgomery, Russell, Southwick and Tolland, in the county of Hampden; and Easthampton and Southampton, in the county of Hampshire.

Stephen Brewer is the incumbent Senator in the Worcester, Hampden, Hampshire and Franklin District, consisting of Ashburnham, Athol, Barre, Brookfield, Charlton, East Brookfield, Hardwick, Hubbardston, New Braintree, North Brookfield, Oakham, Petersham, Phillipston, Royalston, Rutland, Spencer, Sturbridge, Templeton, Warren, West Brookfield and Winchendon, in the county of Worcester; Brimfield, Holland, Monson, Palmer and Wales, in the county of Hampden; Ware, in the county of Hampshire; and Orange and Warwick, in the county of Franklin.