Hooper passed 3,000 Sunday League runs before adding 105 in 14 overs with Matthew Walker. Mark Lathwell earlier hit 87 off 78 balls for Somerset.
Gloucestershire booked their place in the top flight with a comfortable 22-run win over Middlesex at Lord's. Both sides were fighting for a place, each going into the match on 32 points.
Gloucestershire opener Martyn Ball was out for one, caught in the gully by Richard Kettleborough off James Hewitt and captain Mark Alleyne was caught behind for seven by keeper Keith Brown off Hewitt to leave Gloucestershire 19 for two.
But a partnership of 75 between Bobby Dawson and Matt Windows steadied the Gloucestershire ship.
Chasing 197 to win, Middlesex never looked like making the total. A fine 56 from captain Mark Ramprakash offered his team a glimmer of hope but once he was out in the 29th over with the score 111 for four they lost all chance of victory.
Worcestershire secured their place in the First Division with a victory at New Road. Fellow qualifiers Hampshire lost by four runs, having contributed to their downfall with 20 wides among 40 extras in the home side's 181 for nine.
Northamptonshire's Mal Loye made sure of the £5,000 first prize as the AXA League's leading run scorer with 35 in the home side's 89-run victory over Sussex at Wantage Road.
Loye's final tally of 650 runs represents a new Northants record but the win was still not enough to book Kevin Curran's team a place in Division One.
Glamorgan failed to qualify by two points despite beating Derbyshire by 56 runs. Glamorgan's total was built around a fourth-wicket partnership of 112 in 17 overs between Adrian Dale (82) and Michael Powell (55).
Surrey recorded only their third AXA victory of the season, winning the battle of the bottom two by 101 runs at the Riverside but still finishing eight points adrift of Durham.