Yorkshire will begin their Championship season against Leicestershire at Headingley. They may include Harry Brook in their squad, who was unavailable for England's Test tour to India and withdrew from the IPL due to personal reasons.
Joe Root is also expected to join the team for a six-game domestic stint later this month.
Darren Gough, who brought in Ottis Gibson as coach, has stepped down from his role as managing director of cricket, with Colin Graves returning as chairman for a season in which the White Rose look set for a promotion push.
Middlesex will be hoping that the signing of Derbyshire talisman Leus du Plooy will spearhead an immediate return to the top flight, although seamer Tim Murtagh will be watching from the sidelines following his retirement.
Northants, who finished bottom of Division One last season, have added Australian Chris Tremain and India's Karun Nair to their squad for the start of the season. Additionally, Nair's countryman Prithvi Shaw will return in June.
Sussex has seen Ali Orr depart for Hampshire this winter but has strengthened their team with the addition of John Simpson from Middlesex and Lancashire's Danny Lamb. They will also have the talents of West Indies bowler Jayden Seales and India batter Cheteshwar Pujara available early in the campaign.
Leicestershire seamer Chris Wright's contract has been terminated for personal reasons but England paceman Ollie Robinson will be available for the start of the season.
Leicestershire has lost Colin Ackermann and Calum Parkinson to Durham. However, Liam Trevaskis is joining the team. Additionally, Ben Mike and Ben Cox have arrived from Yorkshire and Worcestershire respectively. Furthermore, Scott Currie joins on loan from Hampshire.
Glamorgan have appointed Grant Bradburn as head coach and Sam Northeast as Championship skipper following the departure of David Lloyd to Derbyshire, while Mason Crane has joined Sophia Gardens on a season-long loan from Hampshire. Neser's decision to move in the opposite direction will not aid Glamorgan's chances of finishing in the top two.
Lloyd takes over the captaincy from Du Plooy and is joined at Derbyshire by veteran Patel, as well as Aneurin Donald and Ross Whiteley from Hampshire.
Mark Alleyne has returned to lead Gloucestershire, who failed to win any matches last season. Cameron Bancroft and Beau Webster have signed overseas deals after playing for Somerset and Essex, respectively.