The figures showed a 2% drop in cross border shoppers in the 12 months compared to the previous year, when an estimated €435m was spent.
The CSO said: “While there was a decline in the proportions of households making shopping trips to Northern Ireland, this was offset by the fact that households who were making trips were doing so more than previously.”
Some €311m of the total was forked out by those travelling north specifically to shop, with €107m spent during trips where shopping was not the main purpose but occurred.
More than a third of shoppers were from the border regions, who made 8.6 trips in the year and spent €240m, up from €181m.
While Dubliners still represented 29% of cross border shoppers, they spent just €57m – half of what the tills took in a year earlier. The average last shop spend fell to €284.
But figures revealed the biggest spenders travelled the furthest.
The survey showed while the lowest proportion of shoppers were from the south-east, mid-west and south-west of Ireland – making up just 8% of consumers – they splashed out an average €523 on their last trip. Overall their annual spend was €30m.