| 1862 | Lancaster Town Library established. |
| 1863 | Library Museum established. |
| 1868 | Memorial Hall was dedicated as the Town Library with cabinet room upstairs to be used for the display of historical, natural history and mineralogical collections and ornithological specimens. |
| 1888-89 | Museum room enlarged and new cases added. |
| 1905-06 | The museum was re-arranged, moldings added for hanging pictures, and all bird speciments that were in good shape were sent to the Thayer Museum in South Lancaster. |
| 1913 | The collection of samplers was taken from the Museum and hung on the north wall of the reading room. |
| 1916 | The portrait alcove of the Museum was re-arranged and brass name plates were put on the frames. |
| 1936 | On May 5th, the Board of Trustees voted to make the museum a historical museum and dispose of specimens which did not properly belong in a historical museum |
| 1940 | Under the direction of the Board, Miss Virginia Morley Keyes, the Library Director from 1903 to 1947, had a wooden gate installed at the entryway to the museum. On April 2nd the Board inspected the new gate and pronounced it "satisfactory". |
| 1953 | Under the direction of Herbert H. Hosmer, Jr., the contents of the Musuem were cleaned, rearranged and the walls painted and the museum was opened in time for the 300th anniversary of the Town. |
| 1956 | On November 26th, Mrs. Dorothy Adams Fifield, Library Director from 1951 to 1959, presented a list of new equipment and improvements for the Library that included "whitening" the museum ceiling. |
| 1983 | On April 13th a vote was taken by the Library Trustees and the Lancaster Historical Commission giving the Trustees authority over the museum. The Historical Commission agreed to act in an advisory capacity |
| 1985 | The museum shelves were emptied and used for an exhibit named "A General Diffusion of Knowledge" |
| 1997 | The museums artifacts were packed up and put into secure storage while the building's renovation and expansion took place. |
| 1999 | The Board of Trustees voted to rename the Lancaster Town Library to honor the Thayer family. The re-dedication and opening of the newly renovated Thayer Memorial Library was on Nov. 28, 1999. |
| 2004 | After being closed since 1997, Library Director Joseph Mule, curators, Frank MacGrory and John Schumacher-Hardy, and editor Cecilia E. Thurlow, organized the TML Historical Museum Catalog by documenting over 800 artifacts. |
| 2012 | In celebration of the Library's 150th anniversary the museum was transformed into an exhibit named "A General Diffusion of Knowledge". This was based on the original exhibit of 1985. After the exhibit was dismantled, the museum was closed. Some of the artifacts remained in their original cases while many more were stored in the museum annex. |
| 2014 | During the closure of the museum it suffered water damage due to a leaky roof. After languishing for over a year, a team of volunteers led by Trustee Steve Piazza, started the task of repairing the damage, re-cataloging all of the items and restoring the museum. |
| 2015 | By late spring the museum had been repainted, given a thorough cleaning, re-inventoried and object descriptions were updated. The inventory was captured into a database and made available in both hardcopy in the museum and on-line on the Library's web site. |
