Hello Margaret
I've also done a little digging and discovered that there were three Josiah CARRs in the 1861 census:
The first was born in Bucks circa 1821, is resident in Oxfordshire and has a wife named Charlotte. This must be the Josiah, son of John, who married Charlotte HAMBLEDEN at Lane End on 24 May 1858. He is shown in the 1851 census in Dean Street, Great Marlow, aged 29 years, unmarried, a journeyman shoemaker living with his widowed mother, Ann CARR.
The second Josiah was born in Bucks circa 1840, is resident in Bucks and has a wife named Louisa. This must be the Josiah who married Louisa FORD at Bisham, Berks, on 23 June 1860. The IGI record gives this person's father as Richard CARR, and the baptism of Josia, son of Richard and Hannah CARR is recorded at Great Marlow on 31 Dec 1839. Richard's occupation is given as shoemaker. From his age given in the 1851 census I assume that Richard is the person baptised at Great Marlow on 9 June 1811, the son of John and Ann CARR.
The third Josiah was born in Bucks circa 1817, is resident in Bucks and has a wife named Ruth. This is, in fact, an error as this person is really named Joshua. Joshua CARR married Ruth JIMMOTT at Lane End on 17 Mar 1844.
Although there is no baptism to be found for Josiah circa 1821 at Great Marlow the evidence suggests that he is the son of John and Ann CARR and therefore a brother of the Richard CARR who had a son named Josiah. He does not belong in the family of John and Sophia CARR.
Orpheus