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Mainstreet RIA LLC

O'Fallon, MOSEC-registered investment adviserCRD 309150

Filed as MAINSTREET RIA LLC

Mainstreet RIA LLC is an SEC-registered investment advisory firm in O'Fallon, MO, registered since 2021, reporting $100 million to $500 million in regulatory assets under management in its Form ADV filing dated September 29, 2026.

5 years
registered since 2021
$471,751,580
assets under management
3 arrangements
Percentage of assets, Hourly and more
None
disclosure items (Item 11)

Quick answers

From the filing

How is Mainstreet RIA LLC compensated?

On its Form ADV (Item 5.E, October 2026), Mainstreet RIA LLC reports these compensation arrangements: a percentage of assets under its management; hourly charges; fixed fees (other than subscription fees).

Where is Mainstreet RIA LLC located?

Mainstreet RIA LLC's principal office is in O'Fallon, MO, according to its Form ADV.

Is Mainstreet RIA LLC registered with the SEC or a state?

Mainstreet RIA LLC is an SEC-registered investment advisory firm, registered since 2021. Status as filed: Approved. CRD 309150.

How much does Mainstreet RIA LLC manage?

Mainstreet RIA LLC reports $471,751,580 in regulatory assets under management in its Form ADV filing dated September 29, 2026 (100% discretionary).

How have Mainstreet RIA LLC's assets and staff changed since 2021?

In the Form ADV data for Mainstreet RIA LLC: Regulatory assets under management: $276,500,000 in the October 2021 data and $471,751,580 in the October 2026 data, up 71%. Total employees: 3 in October 2021 and 3 in October 2026. Assets under management move with markets as well as with clients coming and going.

What types of clients does Mainstreet RIA LLC serve?

By number of clients on Form ADV Item 5.D: individuals (other than high net worth individuals) (124); high net worth individuals (12); pension and profit sharing plans (but not the plan participants or government pension plans) (5).

Which custodians does Mainstreet RIA LLC use?

Mainstreet RIA LLC's most recent Form ADV filing (Schedule D, Section 5.K(3)) lists Charles Schwab & Co., Inc. and Corebridge Retirment Services as custodians holding 10% or more of its separately managed account assets.

Does Mainstreet RIA LLC report any disciplinary disclosures?

Reports no disclosure items on Form ADV Item 11. The detail of any item is on the firm's SEC record: https://adviserinfo.sec.gov/firm/summary/309150

Does Mainstreet RIA LLC state an account minimum?

Its Form ADV Part 2A brochure dated February 12, 2026 says: "Mainstreet requires a minimum of $ 250,000 to open an account. In certain instances, the minimum account size may be lowered or waived."

What changed in Mainstreet RIA LLC's recent Form ADV filings?

In the March 2026 filing data: Regulatory assets under management went from $392,246,687 to $446,355,239 (+14%).

From the Form ADV filing

Every figure below is as the firm filed it with regulators, as of October 2026.

How the firm is compensated

Item 5.E
  • A percentage of assets under your management
  • Hourly charges
  • Fixed fees (other than subscription fees)

Item 5.E lists how the firm is compensated for its advice; Items 5.B, 6.A, and 7.A show whether its people or related companies can also earn commissions. Percentage of assets, fixed, hourly, subscription, and performance-based fees come from clients (a performance-based fee depends on investment results); commissions come with a sale or a trade, often from the company behind the product. How fees, commissions, and other arrangements differ

Fees and minimums

Form ADV Part 2A

The brochure lists different fees for different services or strategies; see the brochure for them.

Account minimum: $250,000 (the brochure says it may be waived or negotiated)

The brochure's wording
Mainstreet requires a minimum of $ 250,000 to open an account. In certain instances, the minimum account size may be lowered or waived.

As stated in the firm's Form ADV Part 2A brochure dated February 12, 2026. Fees can differ by service and may be negotiable; the brochure is the complete statement. Read the brochure on the SEC's IAPD site

Regulatory assets under management

Item 5.F
$471,751,580

$471,751,580 as of October 2026, filing dated September 29, 2026.

Discretionary: $471,751,580.Non-discretionary: $0.

A measure of scale, not skill or returns. Discretionary means the firm decides trades; non-discretionary means clients approve each one. What assets under management means

Who the firm serves

Item 5.D
Individuals (other than high net worth individuals)
Clients 124 Assets $47,176,513 (10%)
High net worth individuals
Clients 12 Assets $28,712,367 (6%)
Pension and profit sharing plans (but not the plan participants or government pension plans)
Clients 5 Assets $395,862,700 (84%)

A firm with no individual clients is an institutional manager even if it manages billions; the mix tells you whom the practice is built around.

Advisory services

Item 5.G
  • Financial planning services
  • Portfolio management for individuals and/or small businesses
  • Pension consulting services
  • Educational seminars/workshops

Registration and firm details

Items 1, 2, 5
Registration
SEC-registered investment adviser. Status as filed: Approved.
Registered since
2021 (5 years)
Employees
Total: 3. Performing investment advisory functions: 3.
Wrap fee program participation
No.
Custodians (Schedule D, Section 5.K(3))
Charles Schwab & Co., Inc.Corebridge Retirment Services

Custodians holding 10% or more of the firm's separately managed account assets, as filed on Form ADV (Schedule D, Section 5.K(3)). A custodian holds client assets; it does not endorse or supervise the firm. AdvisorCensus has no relationship with any custodian.

States registered or notice-filed
3 states or jurisdictions
ILMOTX

SEC-registered investment advisers are examined by the SEC. SEC, state, and exempt registration

Disclosures

Item 11

None Reports no disclosure items on Form ADV Item 11. View on IAPD.

Item 11 asks about criminal, regulatory, and civil events involving the firm and its advisory personnel. The detail of each yes answer is on the IAPD record. Reading a firm's disclosures

Assets and staff over time

Items 5.A, 5.F
$276M 2021 $287M 2022 $274M 2023 $375M 2024 $392M 2025 $472M 2026
Data periodAssets under managementEmployeesFiling dated
October 2026$471,751,5803September 29, 2026
October 2025$392,246,6873January 15, 2025
October 2024$374,979,9853July 16, 2024
October 2023$274,296,1103January 18, 2023
October 2022$287,400,0003August 30, 2022
October 2021$276,500,0003September 16, 2021

Regulatory assets under management: $276,500,000 in the October 2021 data and $471,751,580 in the October 2026 data, up 71%.

Total employees: 3 in October 2021 and 3 in October 2026.

As filed in each year's data for the same month. Assets under management move with markets as well as with clients coming and going; they measure scale, not skill or returns. Most firms update these figures once a year.

Changes in the filing

Last 12 months
  1. March 2026
    • Regulatory assets under management went from $392,246,687 to $446,355,239 (+14%).

Compared month to month from the SEC's monthly adviser data and the state compilation feed. Owners and control persons are summarized, never named.

Websites listed on Form ADV

Item 1.I
mainstreet-ria.com

Source: Form ADV, as of October 2026. Values appear as filed; a value the firm did not report is shown as "Not reported."

Cite this page

AdvisorCensus. Mainstreet RIA LLC (CRD 309150): Form ADV filing data as of October 2026.
https://advisorcensus.com/firm/mainstreet-ria-llc-o-fallon-mo-309150