Gustavus Crostons military service records (35 cards or pages), pension record (42 pages), final pension payment card, and muster rolls, where his name appears are on www.Fold3.com (paid research site).
Dear Mr. Croston,
Thank you for posting your request on History Hub!
The records that Ms. Brooks references on Fold3 are digital copies of these series titled Compiled Service Records of Soldiers Who Served in the American Army During the Revolutionary War and Revolutionary War Rolls in the War Department Collection of Revolutionary War Records (Record Group 93); Case Files of Pension and Bounty-Land Warrant Applications Based on Revolutionary War Service, ca. 1800 - ca. 1912 in the Records of the Department of Veterans Affairs (Record Group 15); and Selected Final Payment Vouchers, 1818 - 1864 in the Records of the Accounting Officers of the Department of the Treasury (Record Group 217). While portions of some of these series are available online using the National Archives Catalog, the records pertaining to Gustavus Croston are not yet available.
We also located the series Numbered Record Books in Record Group 93 that includes 6 file units & 1 item pertaining to the 1st Virginia State Regiment. For more information about these records, please contact National Archives at Washington, DC - Textual Reference (RDT1) via email at Archives1reference@nara.gov.
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We hope this is helpful. Best of luck with your research!