Hello Wendy,
You have Wicklow and say ‘it looks like he married in England’. Is the place from the census and marriage based on Sarah’s birth?
Is this your family?
1841 574/16/26
No. 1 Court, Church Street
Dennis Dunn 33 yrs b Ireland
Catherine Dunn 30 yrs b Ireland
Sarah Dunn 5 yrs b in county
Jane Dunn 5 Months b in county
There is
There are possible births for Jane with mother’s names on GRO and also deaths.
There is a death for a Catharine Dunn, 37 yrs in 1846

Marriage 1849 Dennis Dunn and Mary A Kelly (Moore) Lancashire BMD - may be him?
http://www.lancashirebmd.org.uk/index.phpThen 1851
86 Pump Street
Dennis Dunn 38 yrs Weaver b Ballingate, Ireland
Mary Ann Dunn 36 yrs born (dittoed)
Sarah Dunn 15 yrs b Manchester
If it is your family, then the 1849 marriage would give you his father’s name.
Heywood