Have you tried adding # around the date fields?

MySQL = MySQL + "WHERE [tbl_Combined].[RecDate]>=#" & [Forms]![frm_Report_Selection]![StartDate] & "
MySQL = MySQL + "# AND [tbl_Combined].[RecDate]<=#" & [Forms]![frm_Report_Selection]![EndDate] & "
MySQL = MySQL + "# AND [tbl_Combined].[WhoToCount]= 'Family' "

I tried it as you've shown above and it's still ignoring the start and end dates.

Can you Debug.Print MySQL

Yea do a Debug.Print or add a line below that

Msgbox MySQL

and Snip & Sketch it here

Yeah, looks OK. Gotta see it.

The following code worked in the sense that VBA interpreted it correctly. The debug.print view confirmed it.
MySQL = ""
MySQL = "SELECT [tbl_Combined].[Case#], [tbl_Combined].[RecDate] AS [SvcDate], [tbl_Combined].[WhoToCount] "
MySQL = MySQL + "AS [ServiceTo], [tbl_Combined].[key] AS [Ky] INTO [tbl_Combined_FamilySelect] "
MySQL = MySQL + "FROM [tbl_Combined] "
MySQL = MySQL + "WHERE [tbl_Combined].[RecDate]>= #" & [Forms]![frm_Report_Selection]![StartDate] & "#" & " "
MySQL = MySQL + "AND [tbl_Combined].[RecDate]<= #" & [Forms]![frm_Report_Selection]![EndDate] & "#" & " "
MySQL = MySQL + "AND [tbl_Combined].[WhoToCount]= 'Family' "
MySQL = MySQL + "ORDER BY [tbl_Combined].[Case#], [tbl_Combined].[RecDate];"
DoCmd.RunSQL MySQL
The debug.print view won't fit here. I'll submit it next...

debug.print view?
SELECT [tbl_Combined].[Case#], [tbl_Combined].[RecDate] AS [SvcDate], [tbl_Combined].[WhoToCount] AS [ServiceTo], [tbl_Combined].[key] AS [Ky] INTO [tbl_Combined_FamilySelect] FROM [tbl_Combined] WHERE [tbl_Combined].[RecDate]>= #1/1/2021# AND [tbl_Combined].[RecDate]<= #1/31/2021# AND [tbl_Combined].[WhoToCount]= 'Family' ORDER BY [tbl_Combined].[Case#], [tbl_Combined].[RecDate];

The problem I'm having now is inconsistent results. This thing uses Short Dates. Start and End Dates are defined on the form as short dates and all the dates in the db are short dates. Sometimes the query works and other times I get zero results, or the query spits out a table based on the previous start and end dates enterered. It's wierd.

I'm wondering if I need to add something to the VB code to clear out a buffer or something so that the user can enter as many date criteria as they want and rerun the report.

P.S. I run into the same problem when I run this with DoCmd.OpenQuery, so I'm thinking the problem has something to do with the dates.

If you copy that into a new Query SQL view and run it does it work?

Is your field really called Case#?
I'd rename that to CaseNo or CaseNum or CaseNumber

Yeah, that's a good idea, Alex, but as long as he has the brackets, that wouldn't cause the problem. I dunno. Without seeing it in action, it's very hard to tell. Nothing is jumping out at me.

When I run it from the Access query editor (right-clicking on the query and bringing up under SQL design view), I can run it every time correctly. I am prompted to enter the dates as I should and the results are correct entering different dates every time. It's only in VBA that I'm running into the problem, whether as an SQL sting or as DoCmd.OpenQuery.
I noticed when I used debug.print and looked at the SQL in the immediate window that I would see the SQL listed multiple times as I tested--entering different dates multiple times. That's why I was wondering if there was VBA code I have to add that would basically clear out any buffers or storage areas that VBA uses for SQL strings. I made sure MySQL = "". Is there something more I should be doing? Can't find anything about that as I Google for answers.

Oh, OK... I see the disconnect here... you can't use DoCmd.RunSQL to run a SELECT query to view records. RunSQL is only good for action queries (insert, update, delete, etc.) If you want to VIEW these records, you'll need to make a form and then set the RecordSource property of your form to the SQL statement. I didn't realize that's what you were trying to do. Again, that's why it's easier if we can see screen shots of your database. See Record Source Property.

And DoCmd.OpenQuery has to open an actual saved query.