  Houghton's groups $H_2, H_3, \ldots$ have been studied in many contexts, and
various results exist for their finite index subgroups. In this note we
describe all of the finite index subgroups of each Houghton group, and their
isomorphism types. Using the standard notation that $d(G)$ denotes the minimal
size of generating set for $G$ we then show, for each $n\in \{2, 3,\ldots\}$
and $U$ of finite index in $H_n$, that $d(U)\in\{d(H_n), d(H_n)+1\}$ and
characterise when each of these cases occurs.
