Champions Surrey will begin their County Championship title defence at home to 2017 winners Essex at The Kia Oval on April 11.
Vitality Blast champions Worcestershire will kick off their title defence at Notts, with Finals Day set for September 21.
The County Championship will move to a 10-team Division One in 2020 after an agreement was on changes to the structure.
Craig Overton became the second Somerset player in as many days to take a hat-trick as they beat Nottinghamshire at Taunton.
Tom Abell took a remarkable hat-trick as Somerset forced Nottinghamshire to follow on at Trent Bridge.
Essex's Jamie Porter and Sam Cook claimed four wickets each to condemn Surrey to a day to forget at the Kia Oval.
Yorkshire and Hampshire's clash at Headingley ended in a weather-affected draw as no play was possible on day four.
Hampshire, whose safety was confirmed by Worcestershire's defeat at Essex, suffered a rain-affected day against Yorkshire.
Joe Clarke hit an unbeaten 74 as Worcestershire looked to cling on to their slim County Championship survival hopes at Essex.
Hampshire just shaded a bowler-friendly opening day against Yorkshire as 15 wickets fell on day one of their clash.
Alfred the Gorilla's winning run came to an end as Leicestershire's mascot 'outfoxed' the opposition to take the spoils...
Yorkshire secured a 95-run County Championship win over Roses rivals Lancashire to take a huge step towards avoiding relegation.
Morne Morkel edged Surrey closer to a win over Worcestershire and their first County Championship title in 16 years.
Lancashire enjoyed an excellent opening day of their Division One relegation battle with Yorkshire at Headingley.
Surrey's seamers blew away County Championship title-holders Essex as they extended their lead at the top of Division One.
Moeen Ali has credited his maiden T20 century as a catalyst to his England recall after being named PCA Player of the Month.
Keshav Maharaj took 7-37 as his side snatched a dramatic tie in their astonishing County Championship clash with Somerset.
Surrey skipper Rory Burns scored 90 at Essex as he became the first batsman to 1,000 County Championship runs this season.
Mark Stoneman and Ian Bell are in as Surrey and Warwickshire continue their bids to win Division One and Two respectively.
Yorkshire and Hampshire remain in big danger of relegation after comprehensive defeats to Somerset and Essex respectively.
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