The New Democrats made in-roads in the region in the last election, gaining a toehold in a Brampton.
They're looking to expand that this time around, and Horwath's rally Saturday in the city was her second visit there this week.
She attacked scandals surrounding the Liberal government and talked up the NDP's plan to create jobs, but in a break from her stump speech dug into Premier Kathleen Wynne for not cutting auto insurance rates enough.
While the Liberals have cut rates, Horwath says they didn't go as low as promised and cited the case of a "Melinda" from Brampton who saw her rates rise.
Horwath says rates haven't dropped quickly enough despite the Liberal's budget pledge last year to drop them 15 per cent by August 2015.
The province's insurance regulator announced in January that average premiums that quarter were down about four per cent.
The Liberals issued a statement on Saturday accusing Horwath of opposing two pieces of government legislation, one regulating the towing industry, another cracking down on auto insurance fraud, that they contend would have led to lower insurance rates.
The campaign event was Horwath's only election stop Saturday, and she is to fly to the province's north — where the NDP holds several seats — on Sunday.