Some of this is due to an ageing population and some to a rising share of that population in the labourforce: the so-called participationrate has jumped a percentage point, to 40%, while slipping for the population as a whole.
The participationrate, the share of the labourforce either working or looking for work, has declined steadily since 2007, though it ticked up ever so slightly in September, to 63.6% (see chart).
The unemployment number just looks at those actively looking for work, therefore if labourforceparticipation stays low it will only take modest job growth to be responsible for the unemployment rate to enjoy a significant decline.