Several ways of collecting information were used to complete the data form for each principal structure surveyed (see a sample survey form in Appendix B). The surveyor recorded most items through observation in the field — use, architectural style, description of architectural features, any alterations, and an estimated date of construction based on prevalent architectural styles and building types and when they commonly appeared in Illinois. Available building history information from Village of Libertyville records, the Cook Memorial Public Library, and the Libertyville-Mundelein Historical Society was used to verify construction and alteration dates. Information from these sources was recorded on the back of the forms. Other published texts, newspaper articles and Sanborn Fire Insurance Maps, walking tours, and locally prepared lists were also consulted. These are listed in the bibliography. Additional information for several homes was obtained through house histories solicited from owners by the consultant.
The main sources used to determine architectural styles were A Field Guide to American Houses by Virginia Savage McAlester (2013) for high-style architecture and Common Houses in America’s Small Towns: The Atlantic Seaboard to the Mississippi Valley by John A. Jakle, Robert W. Bastian, and Douglas K. Meyer (1989) for vernacular building types. Descriptions of specific architectural features relied on the Old-House Dictionary by Steven J. Phillips (1989).
In the field, the surveyor made a judgment on the integrity and the significance of each structure based on specific evaluation criteria. The survey forms were later reviewed in the office so that an individual building could be evaluated within the context of the city as a whole. The members of the Libertyville Historic Preservation Commission also had the opportunity to review the survey data before they were finalized.
All principal buildings in the area surveyed were evaluated for local architectural significance using the criteria for architectural significance as stated in the Libertyville Historic Preservation Ordinance. Each building was determined as either a contributing (C) or non-contributing (NC) resource within a potential historic district comprised of the survey area. Each building was also evaluated for eligibility for listing as an individual local landmark—those buildings that were eligible were identified in the “Local Landmark Eligible?” field. Also identified were “Potentially Eligible” buildings—properties that featured more than minor alterations, but still may be eligible for local landmark designation based on their historic importance or special architectural features or rarity. With these potentially eligible properties, the Commission can use its discretion to consider local landmark designation.
Next, all principal and secondary structures on a property were analyzed for potential National Register listing. A "Y" (Yes) indicates that the surveyed building likely would be a good candidate for individual listing on the National Register (or, in some cases, has already been listed on the National Register). An "N" (No) indicates that it would not. “Criteria” refers to the National Register criteria that were considered. Only criterion “C,” architectural significance, was used in evaluating potential National Register eligibility. Criteria “A” and “B,” which refer to historical events and persons, were not considered. For the question of contributing to a National Register district, a "C" building would be a good contributing building in a National Register historic district. An "NC" building would not.
Integrity, that is, the degree of original design and historic material remaining in place, was factored into the evaluation. In general, no building was considered eligible for local landmark designation if it had more than minor alterations. Exceptions were made for those significant properties that had been restored or rehabilitated, as well as properties with historic alterations. Similarly, buildings that might otherwise be considered contributing to a potential historic district because of age and historic style, but that have been greatly altered, were ranked as non-contributing to a potential historic district. Buildings were evaluated primarily for their architectural significance, with historical significance, known in only a few cases, being a secondary consideration. It is possible that a building could be elevated to a locally significant ranking and thus considered for individual local landmark designation by the Historic Preservation Commission if additional historic research identifies an association with important historical figures or events. For some buildings whose significant historic features have been concealed or altered, they might also be re-ranked as locally significant if unsympathetic alterations are removed and significant historic features restored.
Architectural integrity is evaluated by assessing what alterations to the original historic structure have occurred. Structures were considered unaltered if all or almost all of their historic features and materials were in place. Minor alterations include replacement siding, replacement windows in original openings with historically-appropriate type and configuration; minor porch alterations or enclosures, and rear additions. Moderate alterations could also include side additions and more substantial porch changes, but with porch structure still essentially intact. Major alterations include irreversible changes and large additions. These include porches and other architectural detailing that have been completely removed or replaced and for which there is no actual physical evidence or photo documentation to accurately reproduce them; window changes in which the original window opening size has been altered and there is no evidence of the original sash configuration and material; and large unsympathetic additions, visible from the street, that compromise the historic character of a house by changing the original roofline or obscuring or substantially altering the façade.
NATIONAL REGISTER RATINGS
A. INDIVIDUAL LISTING (Y)
Must be a site, building, structure, or object that is at least 50 years old (unless it has achieved exceptional significance) and meets one of the following criteria: (a) be associated with events that have made a significant contribution to the broad patterns of our history; (b) be associated with the lives of persons significant in our past; (c) be architecturally significant, that is, embody the distinctive characteristics of a type, period, or method of construction, or represent the work of a master, or possess high artistic values. It must also possess integrity of location, design, setting, materials, workmanship, feeling, and association from the date of construction or period of significance.
B. CONTRIBUTING TO A HISTORIC DISTRICT (C)
Age. Must have been built or standing during the period of historic significance or be at least 50 years old or older (built before 1966).
Integrity. Any building that possesses enough integrity to still be identified with the period of historic significance.
C. NON-CONTRIBUTING (NC)
Age. Any building or secondary structure built after the period of significance or less than 50 years old (built in 1967 or later).
Integrity. Any structure that has been so completely altered after the period of significance that it is no longer recognizable as historic.
LOCAL SIGNIFICANCE RATINGS
A. LOCAL LANDMARK ELIGIBLE
Age. Must be at least 50 years old or older (built before 1966) OR must be listed on the National Register of Historic Places
Architectural Merit. Must meet at least one of the criteria for landmark designation set in Libertyville’s Historic Preservation Ordinance.
B. POTENTIALLY ELIGIBLE (FOR LANDMARK DESIGNATION)
Age. Must be at least 50 years old (built before 1966) unless it has achieved exceptional importance.
Architectural Merit. See criteria for Local Landmark Eligible
Integrity. Must have a moderate degree of integrity; if it has been altered, it should be in ways that can be reversed: some architectural detailing in place so that missing exceptional features could be recreated; porch alterations are minor; and window changes should be reversible; no large, unsympathetic additions permitted. If the alterations are reversed (for example, siding is removed, or architectural detail is restored based on remaining physical evidence), it may be elevated to significant. In some cases of exceptional architectural or historical merit, side additions or permanent alterations were considered acceptable and the PS rating was assigned.
C. CONTRIBUTING TO A POTENTIAL HISTORIC DISTRICT (C)
Age. Must be at least 50 years old (built before 1966).
Architectural Merit. May fall into one of two groups: (a) Does not necessarily possess individual distinction, but is a historic building (over 50 years old) with the characteristic stylistic design and details of its period; or (b) possesses the architectural distinction of a significant structure but has been altered. If the alterations are reversed (for example, siding is removed or architectural detail is restored based on remaining physical evidence), it may be elevated to significant.
Integrity. May have a high degree of integrity, but be of a common design with no particular architectural distinction to set it apart from others of its type. May have moderate integrity: if it has been altered, it must be in some ways that can be reversed. Must possess at least one of the following: original wall treatment, original windows, interesting architectural detail, and readily recognizable and distinctive historic massing.
D. NON-CONTRIBUTING (NC)
Age. Most buildings less than 50 years old (built in 1967 or later).
Integrity. Any building at least 50 years old whose integrity is so poor that most historic materials and details are missing or completely covered up or any building over 50 years old that has unsympathetic alterations that greatly compromise its historic character. Poor integrity was present if all of these factors were missing: original shape, original wood siding, original windows (especially if window openings were also changed), and original architectural detail and trim.
 Information provided by Ramsey Historic Consultants