I'm not sure where their marriage took place at all.
The information I've got is from their daughter's marriage and death certificates - Annie Templeton Walker. Her marriage certificate (13/07/1872, St. Anne's Church of Ireland, Belfast) states her father as Henry Walker (Carpenter), it doesn't list her mother. Her death certificate (08/09/1914, Govan, Glasgow) states her father as Henry Walker (Farm Labourer) (Deceased) and her mother as Jane Walker, M.S. English (Deceased); although the informant on this death certificate is Annie's son, John Thomson, who I suppose might have mixed up names or not known real names. This is possible as he is also the informant on his father's death certificate, where he lists his (paternal) grandfather as John Thompson, whereas his father's marriage certificate (probably more reliable for accuracy) lists that person as Hugh Thompson.
What I'm not sure if is what to do if, for example, Jane's maiden surname wasn't English at all... how do you go about finding the "real" name/person?