Following are the instances of Lay Arahants that I'm aware of;
What are the other instances of lay arahants (excluding Paccekabuddhas) in the recorded history?
Ven Bahiya. Buddha proclaimed him great disciple of fast learner of Dhamma. He reached enlightenment while was a lay person, however, he was killed while looking for personal items to join the Sangha. Buddha classified him as one of the 41 great Bhikku.
In the Soṇa Sutta 1 (S 22.49), the Supreme Buddha teaches Soṇa the houselord‘s son of Rājagaha, a teaching usually given to monastics. At the end of the discourse, Soṇa the houselord‘s son becomes an arhat . https://suttacentral.net/en/sn22.49
Laymen arhants are very rare. No sooner they attain Nibbana, if they do not join the order of Sangha, they are unable to live as lay disciples and they attain parinibbana. In the The Gilāyana Sutta (S 55.54), Buddha tells how a lay follower in his/her deathbed can become a Arahant. And the lay followers liberation (while in his deathbed) is no different to that of a monk. http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/4.10-Mahanama-Gilayana-S-s55.54-piya.pdf
Also I have heard of a mention in one of the suttas, as to how a king became an Arahant while resting. His queen (wife) was fanning him first and gives the task to a servant girl. It was the rhythm of her bangles was the trigger that awakened him. No sooner I find the reference to this, I will post it.