The average Briton has just under £8,000 saved in a tax-free account - the equivalent of almost a third of typical annual earnings, research has revealed.
Savers have an average of £7,782 stashed away in an ISA, while people in some areas of the country have saved more than £10,000, according to Halifax.
Those from the Derbyshire Dales are the best ISA savers, boasting average account balances of £10,476, followed by those in South Buckinghamshire at £10,341.
More than 50% of the top 30 local authorities where people have the highest levels of ISA savings are in Greater London and the South East.
However those in the London boroughs of Southwark and Hackney have the lowest levels of ISA savings - at an average of £4,791 and £4,675 respectively.
On a regional basis, people in East Anglia have saved the most, at an average of £8,366, followed by those in the East Midlands at £8,340.
At the other end of the scale, people in Scotland have an average of just £6,453 set aside in a tax-free account, with those in the South West having saved £7,590.
But when savings levels are looked at in terms of average local earnings, people in Wales are the best savers, with the equivalent of 37% of local pay deposited in an ISA, followed by those in Northern Ireland at 36%.
Londoners save the least as a proportion of their pay, holding the equivalent of 21% of average local earnings in an ISA.