I am advised by Revenue that taxpayers are not required to declare their citizenship on Income Tax returns, therefore statistics relating specifically to Irish citizens are unavailable.
The overall numbers of taxpayers paying at each Income Tax rate, and those who are exempt from paying Income Tax, are available at link: https://www.revenue.ie/en/corporate/information-about-revenue/statistics/income-distributions/income-earners-it.aspx.
The same information for USC is available at link: https://www.revenue.ie/en/corporate/information-about-revenue/statistics/income-distributions/income-earners-usc-rates.aspx.
The information provided above shows information up to 2016, the most recent year for which tax returns are filed and processed. However, projections for 2019 are included in the Revenue Reckoner on page 3 at link: https://www.revenue.ie/en/corporate/information-about-revenue/statistics/ready-reckoner/index.aspx.