Merthyr council said 977 people were tested for coronavirus during Wales’s first day of mass-testing.
However only nine people tested on Saturday were found to have Covid-19.
Up to 175 armed forces personnel were drafted in to help as people queued at Merthyr Tydfil Leisure Centre.
It comes weeks after the area was given the title of the worst affected place in the UK. Latest figures showed it had 250.3 cases per 100,000 of the population over a seven-day period.
This places it behind Blaenau Gwent (396.5) and Neath Port Talbot (258.9).
Anyone living or working in the county can now get a test and up to 60,000 people could be tested in total, with those without symptoms also urged to take a test.
Merthyr council has revealed the full list of testing sites and their opening times.
It has also created a regional helpline for those who test positive or were contacted by tracers and told to self-isolate.
There are concerns some could be left hard up if told to self-isolate weeks before Christmas.
The Welsh Government has set up a payment scheme for those on low wages.