CO Donegal has emerged as the most likely landing area for the meteorite that crashed to earth last Wednesday evening.
Tens of thousands of people saw the fireball as it crashed through the atmosphere above Ireland at around 6pm.
Initial reports suggested it had landed in Cavan, but these have since been discounted.
Experts at Astronomy Ireland, who have been collating eye-witness reports, are preparing to make an announcement of its likely landing place at a public lecture in Trinity College Dublin this evening.
David Moore of Astronomy Ireland revealed yesterday that the north-west was emerging as the front-runner.
"We are still doing analysis and will be doing it all day tomorrow," he said. "But by tomorrow night we should have a good idea.
"From what we know already, Donegal seems to be the most likely drop area," he said.
"At this stage there is a 50/50 chance that Donegal is the correct county, so if you are living in Donegal you should be going on long country walks and keeping your eyes peeled."
But he added that they were still urging eye-witnesses to report what they saw on the Astronomy Ireland website.
"It is very important that people in the north-west in particular fill out the report. To date we have 1,000 accounts but it is not enough.
"We estimate that 70,000 witnessed the event. We have always found that only a few per cent of people ever fill out the report forms," he said.
He added that they were also seeking live footage of the event from security footage that would include a part of the horizon.
"So far we have had zero footage of the event. We are urging people to look back over security footage recorded at around 6pm last Wednesday," Mr Moore said.
"One piece of footage is worth about 100 eye-witness accounts in terms of being able to pinpoint with accuracy where it landed."
Tonight's announcement, which will be distributed to Friends of Astronomy Ireland through its website, is expected to prompt thousands of meteorite hunters to descend on Co Donegal, Mr Moore said.
"We are not going to go looking for it ourselves before we announce it. We want a free-for-all," he said.
"When the last meteorite fell to Ireland in 1999 we said it had landed in south Co Wicklow or north Co Carlow and it was found within 20 miles of that area."
The fallen meteorite could range from the size of a football to that of a car, and may have fragmented or remained whole.
The fragments that were found in Co Carlow, which in total would fill a mug, eventually sold for $500 a gram on the internet.