English collective nouns and their agreement patterns have received a great deal of attention in corpus linguistics. Previous synchronic research has found evidence of variability within and across the varieties of English (e.g., Levin 2001, Depraetere 2003, Hundt 2006). This diachronic study compares the agreement patterns with collective nouns in American and British English (henceforth AmE and BrE respectively) and draws evidence from the Corpus of Historical American English (COHA), the Old Bailey Corpus (OBC) and the Corpus of Late Modern English Texts (CLMET). The study covers the time span 1810–1909 and includes the agreement patterns of a range of collective nouns from six semantic domains: (1) EMPLOYEES (e.g., crew), (2) FAMILY (e.g., couple), (3) MILITARY (e.g., army), (4) POLITICS (e.g., government), (5) PUBLIC ORDER (e.g., police) and (6) SOCIETY (e.g., generation).

The results show an overall increase of singular agreement in both varieties. Moreover, the findings suggest that verbal and pronominal agreement patterns behave differently in that the latter is more likely to be of the plural kind, and that variation between singular and plural agreement exists even amongst the semantic categories. The incipient change in AmE towards the singular is visible in the 19^th-century material. The expected leading role of AmE in this change (cf. Collins 2015: 29) could not be confirmed. Instead, AmE displays signs of a kick-down development (Hundt 2009a: 33) in which BrE shows a greater tendency for the singular in the 19^th century, but is overtaken by AmE at a later point in time.