This is more than at any time since 1970, the year in which Saatchi & Saatchi launched.
The figure is well up on 2005, when 15,751 people were working in 240 IPA shops.
It is also a dramatic transformation from the recession-ravaged year of 1993, when a record low number of just over 11,000 people were employed at 225 agencies.
IPA executives say the rise has been spurred by the arrival of 18 new agencies within the IPA. However, they point out that the 10.2% jump in the employment level suggests real growth is taking place.
Hamish Pringle, the IPA director-general, said: "These figures reflect the growth in the number of new sectors in IPA membership -- digital for example."
The news will add to the optimism within the industry, which was encouraged by last week's Bellwether Report predicting that 2007 will show the highest rise in adspend for seven years.
The latest census shows the industry's workforce is split almost 50/50 between men and women. This balance does not extend to boardrooms, where just 14.7% of senior executives are female.
And while the UK population as a whole grows older, adland remains young. Almost half the industry's employees are under 30. Their average age is 33.4 years.
With 7.3% of workers from ethnic minorities, the UK ad business is broadly representative of the national ethnic mix.
- More than 12,700 people work in 201 creative, full- service and other non-media agencies, while 4,655 are employed in 57 media agencies
- About 4.1 per cent of the workforce are part-timers. About 1.6% of people work regularly from home
- IPA agencies employ more than 1,150 freelancers. Almost 45% of them are creatives
- Four out of 10 IPA agencies employ fewer than 25 people. Only 7.8% of agencies have more than 200 staff
- Four per cent of agency staff are first-year trainees
- The proportion of staff from ethnic minorities rose by just 0.4% on last year