Morton Arboretum
A public botanical garden, outdoor museum, research institution, and conservation organization centered on living trees in Lisle, Illinois.
Last updated August 24, 2026
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Overview
The Morton Arboretum is a nonprofit botanical garden and outdoor museum in Lisle, Illinois, devoted primarily to trees, woody plants, ecological restoration, education, and conservation. Founded on December 14, 1922, by Joy Morton, founder of Morton Salt Company, it developed from the Morton family's Thornhill estate and surrounding farmland into one of the largest tree-focused public institutions in the United States. The arboretum occupies approximately 1,700 acres and combines extensive living collections with restored natural areas, gardens, trails, visitor facilities, scientific research, and public programming. Its collections contain more than 4,100 plant species and over 200,000 cataloged plants. The grounds include internationally significant collections of trees and shrubs, a restored tallgrass prairie, woodlands, wetlands, gardens, and naturalized landscapes. Visitors can use roughly 16 miles of hiking trails and nine miles of roads for driving and bicycling. Major visitor amenities include an interactive children's garden, a maze, the Sterling Morton Library, the Thornhill Education Center, and a visitor center completed in 2004. The institution's identity is broader than that of a conventional garden or recreation venue. Through its Center for Tree Science, more than 30 scientists work on urban forestry, tree biodiversity, ecosystem restoration, forest management, and conservation of threatened tree species. Its Global Tree Conservation Program coordinates research and field partnerships focused on rare trees, with particular emphasis on oaks. The Global Conservation Consortium for Oak, a partnership with Botanic Gardens Conservation International, is based at the arboretum. The International Union for Conservation of Nature has also designated the arboretum as its Center for Species Survival: Trees. The arboretum has played a notable role in Midwestern ecological restoration. The Schulenberg Prairie project began in 1962 on former agricultural land and became one of the Chicago suburban region's major restored prairies. The project sought to recreate local prairie composition, structure, and genetic provenance, and involved Ray Schulenberg, Floyd Swink, Robert Betz, and David Kropp. The organization also operates the Chicago Region Trees Initiative, founded in 2014 to address urban tree-canopy loss and uneven access to healthy trees through research, training, public-sector collaboration, planting programs, and policy resources. Education is a central operating area. Programs serve children, families, schools, scouts, adults, restoration practitioners, and other tree professionals. Natural Areas Conservation Training courses provide classroom and online instruction in ecological restoration, while the arboretum also offers credit courses through the Associated Colleges of the Chicago Area. Its Plant Clinic gives the public horticultural and tree-care guidance; in 2024, it reportedly answered more than 15,000 questions from callers and correspondents worldwide. The Sterling Morton Library supports research with books, periodicals, botanical art, nursery catalogs, photographs, landscape plans, institutional records, and special collections relating to Midwestern ecology and landscape history. The Morton family shaped governance during the institution's first decades, but the arboretum is now governed by an independent volunteer board of trustees. Its long-term public profile combines scientific authority, conservation leadership, outdoor recreation, cultural programming, and accessible interpretation of trees and landscapes. Since 2013, the annual Illumination event has extended the visitor season with a nighttime display of tree-focused lighting along a landscaped route. The arboretum remains an active public institution rather than a commercial product brand, with its principal offerings consisting of collections, experiences, research, education, advice, and conservation services.
History
The Morton Arboretum was created by Joy Morton on December 14, 1922. Morton, whose father Julius Sterling Morton was associated with the origins of Arbor Day, had founded the Morton Salt Company and developed the Thornhill estate in Lisle beginning in 1910. The estate's 175 acres formed the initial core of the arboretum, which expanded through additional land acquisition and the conversion of former farmland and other properties into collections and natural areas. Clarence E. Godshalk served as the first superintendent and guided the early planning of the grounds. After Joy Morton's death in 1934, his daughter Jean Cudahy Morton joined the board's leadership. The Morton family continued to influence governance for several decades through Sterling Morton and then Suzette Morton Davidson. In 1977, Davidson retired as the last Morton family board member to serve in that line of leadership, and Charles C. Hafner III became the first chair from outside the Morton family. The institution developed an educational mission alongside its horticultural work. In 1940, Jean Cudahy hired May Theilgaard Watts, who helped establish an extensive program linking nature study, art, and public education. The family also requested an educational center on the site of the Morton home. Much of the residence was demolished in the early 1940s after Margaret Morton died, but Joy Morton's former library survives as the Founder's Room in the Thornhill Education Center. A defining ecological milestone came in the late 1950s and 1960s. Godshalk proposed a native planting on farmland along the arboretum's western boundary, intended to create a landscape buffer and restore prairie. Ray Schulenberg led the project beginning in 1962, working with taxonomist Floyd Swink, biologist Robert Betz, and landscape architect David Kropp. Their approach emphasized local seed sources and the reconstruction of prairie structure, species composition, and local gene pools. The resulting Schulenberg Prairie became one of the region's most important restored tallgrass landscapes. The arboretum expanded its research and reference infrastructure over time. The Sterling Morton Library, designed by architect Harry Weese and completed in 1963, became a major repository for plant science, horticulture, landscape design, Midwestern ecology, botanical art, and institutional history. The library's special collections include materials connected with May Theilgaard Watts, Jens Jensen, Marshall Johnson, O. C. Simonds, and Donald Culross Peattie. A 36,000-square-foot visitor center designed by David Woodhouse Architects opened in 2004 and incorporated sustainable construction features, including permeable paving and salvaged local fieldstone. Administrative leadership passed through four principal executive eras: Clarence Godshalk from 1939 to 1966, Marion Trufant Hall from 1966 to 1990, Gerard T. Donnelly from 1990 to 2022, and Jill Koski beginning in 2022. During the modern period, the arboretum strengthened its role as a scientific and conservation institution. The Center for Tree Science conducts work on urban trees and forests, restoration, management, biodiversity, and threatened species. The Global Tree Conservation Program works with international partners, especially on rare trees and oaks, while the arboretum hosts the Global Conservation Consortium for Oak and the IUCN Center for Species Survival: Trees. Its regional role also broadened through the Chicago Region Trees Initiative, established in 2014 after a regional tree census identified uneven canopy coverage and threats to urban trees. The initiative works with agencies, civic organizations, and other partners on planting, training, policy, data, research, and investment priorities. Public service remains visible through the Plant Clinic, which provides free tree and plant advice, and through educational offerings for families, schools, professionals, and restoration practitioners. Since 2013, the annual Illumination event has added a seasonal nighttime visitor experience. Today the Morton Arboretum functions simultaneously as a living collection, museum, research center, conservation organization, educational institution, and public landscape.
- 2022
Jill Koski becomes president and CEO
[1]Jill Koski succeeded Gerard T. Donnelly as the institution's chief executive.
- 2014
Chicago Region Trees Initiative founded
[1]The arboretum created a regional urban-forestry partnership to improve tree canopy, policy, planting, and data-driven investment.
- 2013
Illumination begins
[1]The arboretum introduced its annual winter tree-lighting event along a paved route through the grounds.
- 2004
Visitor Center opens
[1]A 36,000-square-foot visitor center opened with sustainable design elements and expanded public facilities.
- 1963
Sterling Morton Library completed
[1]The Harry Weese-designed library opened as a center for botanical, horticultural, ecological, and historical collections.
- 1962
Schulenberg Prairie restoration begins
[1]Restoration began on former farmland using locally collected prairie seed and ecological reconstruction principles.
- 1940
Nature and art education program expands
[1]May Theilgaard Watts joined the institution and developed a substantial program connecting nature study and art.
- 1922
Arboretum established
[1]Joy Morton established The Morton Arboretum as a public botanical and educational institution.
- 1910
Thornhill estate established
[1]Joy Morton's 175-acre Thornhill estate later became the founding core of the arboretum.
Products and positioning
A science-led public arboretum that connects living tree collections, ecological restoration, conservation research, urban forestry, education, and outdoor cultural experiences.
Botanical collections · 1922
Living Collections
The arboretum's core collection comprises more than 200,000 cataloged plants representing over 4,100 species and cultivated varieties. It emphasizes trees and woody plants while also incorporating gardens and other living plant collections. The collections support public interpretation, horticultural practice, scientific study, conservation, and comparison of plant performance in the Midwest.
Ecological restoration site · 1962
Schulenberg Prairie
Begun in 1962, Schulenberg Prairie is a large restored tallgrass prairie created on former agricultural land. The project used locally gathered seed and sought to reproduce the composition, structure, and local genetic character of nearby natural prairies. It remains both a visitor landscape and a significant example of Midwestern restoration practice.
Research program
Center for Tree Science
The Center for Tree Science conducts research on urban trees and forests, ecosystem restoration and management, tree biodiversity, and conservation science. Its work links scientific investigation with practical guidance for communities, land managers, and conservation organizations.
Conservation program
Global Tree Conservation Program
This international program combines research, conservation action, and collaboration to protect rare and threatened tree species. It has a particular focus on oaks and supports work with partners in regions including Mesoamerica and parts of Asia. The arboretum also hosts the Global Conservation Consortium for Oak and the IUCN Center for Species Survival: Trees.
Urban forestry program · 2014
Chicago Region Trees Initiative
The initiative coordinates public agencies, civic organizations, and other partners to improve the Chicago region's urban forest. Activities include tree planting, professional training, canopy research, policy resources, collaboration, and data-supported guidance on where investment and protection are most needed.
Public advisory service
Plant Clinic
The Plant Clinic provides free public assistance on tree and plant health, identification, diagnosis, and care. It complements the arboretum's online plant information and seasonal Plant Health Care Report and serves audiences beyond the local visitor base.
Seasonal visitor event · 2013
Illumination
Illumination is an annual late-autumn and winter event featuring coordinated lighting along approximately a mile of curved, paved pathway. Introduced in 2013, it extends the arboretum's visitor season and presents trees and landscapes through a nighttime cultural experience.
Marketing campaigns
- 2014Chicago Region Trees Initiative
Chicago metropolitan region
The initiative brought together public agencies, civic groups, and other organizations to address uneven tree canopy, tree loss, and urban-forestry capacity.
Outcome. It developed planting, training, research, data, collaboration, and policy-support activities for the regional urban forest.
- 2013Illumination
United States
The arboretum began an annual tree-lighting experience designed to interpret the landscape after dark and attract visitors during the winter season.
Outcome. The event became a recurring seasonal program along a dedicated route through the grounds.
Brand decisions
2014
Regional urban-forestry strategy launchedStrategyBackground
A Chicago-region tree census identified gaps and threats affecting the area's tree canopy.
Action taken
The arboretum established the Chicago Region Trees Initiative to coordinate planting, research, training, policy resources, and public-sector collaboration.
Aftermath
The organization expanded its role from site-based horticulture and conservation into metropolitan-scale urban forestry.
1962
Commitment to tallgrass prairie restorationStrategyBackground
The arboretum sought to create a native landscape buffer on farmland acquired near its western boundary.
Action taken
It assigned Ray Schulenberg to develop and implement a restoration based on local prairie species, structure, and seed sources.
Aftermath
The resulting Schulenberg Prairie became a major restored prairie and an enduring part of the arboretum's conservation identity.
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