Using a non-standard port using Microsoft.Data.SqlClient

Connection string

This Microsoft SqlClient Data Provider for SQL Server connection string can be used for connections to SQL Server 2019, SQL Server 2017, SQL Server 2016, SQL Server 2014, SQL Server 2012, SQL Server 2008, SQL Server 2005, SQL Server 2000 and SQL Server 7.0.

If your SQL Server listens on a non-default port you can specify that using the servername,xxxx syntax (note the comma, it's not a colon).

Server=myServerName,myPortNumber;Database=myDataBase;User Id=myUsername;
Password=myPassword;

The default SQL Server port is 1433 and there is no need to specify that in the connection string.