The Federation of Wholesale Distributors, which runs the annual event as part of its My Shop Is Your Shop initiative, said 4,000 retailers donned special t-shirts and caps and decorated their stores with balloons and window stickers, using free NID kits produced for the day.
Thousands of other retailers put on their own special promotions, or displayed the ten brands featured in a Daily Mirror/Daily Record money-off coupon promotion to celebrate the day, which fell on 1 June.
The coupons were redeemed at thousands of stores on the back of the mass circulation of the tabloids involved.
Monitoring of consumer media coverage for the day is not yet complete, but the campaign hit many of its local media targets through regional commercial and BBC radio and TV.
Alan Toft, who chairs the FWD's PR Action Group, said that media emphasis was switched from national news programmes to regional and local media under a new strategy based on the belief that NID was a local story connecting local listeners and viewers to local situations.
He added: "We have a modest five-figure budget for the activity and we have created a massive amount of positive noise this year on behalf of independents.
"Accumulatively, since the launch of MSIYS in 2004, the campaign has achieved millions of consumer hits with positive messages about sole traders and family businesses - the core customer base of every wholesaler in the UK."
The Today's Group chose the day for the official opening of its first Today's Extra store in Hull.
The 2,500 sq ft convenience store, based just off the Hull University campus, began life as two individual buildings that were renovated and refurbished.
Today's Group MD Rodney Hunt said: "This store, the first of its kind within the Today's symbol group, has been designed and fitted to the highest standard with vibrant Today's Local imagery and striking red fascia.
"National Independents' Day was the perfect occasion on which to launch it."