I don't know if this is the same Thomas Darcy or not:

"DARCY, 4 November 1626.

Thomas Darcy was created by king Edward the sixth 5 April 1550 lord Darcy. Thomas, third lord Darcy, was created by king James the first 5 July 1621 viscount Colchester, and by king Charles the first earl of Rivers, with remainder to Thomas Savage lord viscount Savage, his son in law. The titles became extinct in this family at his death 21 February 1639"

Here's a link to Elizabeth Darcy's entry.

All of them are from the Exting Peerage of 1790