Exhibit 21.1

Subsidiaries of the Registrant

Name of the Subsidiary | State or Other Jurisdiction of Incorporation or Organization
Advanced GeoServices Corp. | Pennsylvania
Analytical Environmental Services | California
CTEH Government Services, LLC | Arkansas
CTEH IT Services, LLC | Arkansas
CTEH Leasing, L.L.C. | Arkansas
CTEH Properties, L.L.C. | Arkansas
Emerging Compounds Treatment Technologies, Inc. | Massachusetts
Enthalpy Analytical, LLC | Delaware
Environmental Alliance, Inc. | Delaware
Environmental Intelligence, LLC | California
Environmental Planning Specialists, Inc. | Georgia
Environmental Standards, Inc. | Pennsylvania
Epic Environmental Pty Ltd | Australia
ES Engineering Services, LLC | Delaware
FRS Environmental Remediation, Inc. | Florida
Horizon Water and Environment, LLC | California
Huco Consulting, Inc. | Texas
Leymaster Environmental Consulting, LLC | California
Montrose Air Quality Services, LLC | Delaware
Montrose Environmental Group AB | Sweden
Montrose Environmental Group GmbH | Germany
Montrose Environmental Group Ltd. | British Columbia
Montrose Environmental Group BV | Belgium
Montrose Environmental Group Denmark ApS | Denmark
Montrose Environmental Solutions Canada Inc. | Alberta
Montrose Environmental Solutions, Inc. | Delaware
Montrose Foreign Holdings, Inc. | Delaware
Montrose Government Solutions, Inc. | Delaware
Montrose Measurements and Analytics, LLC | Delaware
Montrose Planning & Permitting, LLC | Delaware
Montrose Services, LLC | Delaware
Montrose Waste-To-Resources, LLC | Delaware
Montrose Water and Sustainability Services, Inc. | Delaware
MSE Group, LLC | Texas
PARS Environmental, Inc. | New Jersey
SensibleIOT, LLC | California
Spirit Environmental, LLC | Texas
Sustainable Treatment Solutions, Inc. | New York
The Center for Toxicology and Environmental Health, L.L.C. | Arkansas

TriAD Environmental Consultants, Inc. | Tennessee
Two Dot Consulting, LLC | Colorado